CHEMICAL REACTIONS

1. What is chemical reaction?
- The breaking down of the old chemical bond and formation of a new chemical bond so as to form new substances with new properties is known as chemical reaction.

2. Define word equation, formula equation and balanced chemical equation. 
- Word equation is defined as an equation in which  the name of chemical substances is written.
Example: Hydrogen+oxygen------> water
- Formula equation is defined as an equation of a chemical reaction expressed in short form by a chemical formula.
- Example: H₂  +  O₂ ------>  H₂O
-Balanced chemical equation is defined as an equation in which the total number of each element in the reactants and products are equal is called a balanced chemical equation.
- Example:  2H₂  +  O₂ ------>  2H₂O

3. What are the factors affecting chemical reaction?(any 4)
- The factors effecting chemical reaction are:
1. Contact- When substance comes in direct contact chemical reaction occurs.
2. Heat- It increases K.E. and hence, increases capacity by colliding with other atom.
3. Light- Light energy makes the reacting atoms reactive and helps to react faster.
4. Catalyst- The chemical substance which increases or decreases the rate of chemical reaction is called a catalyst. A promoter increases power of catalyst.

CLASSIFICATION OF ELEMENTS.

1. Define periodic table and write it's founder.
- A chart in which elements are arranged systematically on the basis of their similarity and dissimilarity in periods and groups is called periodic table.

2. Define  periods and group.
- The horizontal rows of a periodic table are called periods. They are seven in number.
- The vertical columns of a periodic table are called groups. Thy ar eighteen in number.

3. State Mendeleev's Periodic law.
- Mendeleev's Periodic law states that, the physical and chemical properties of elements are the periodic functions of their atomic mass.

4. What are the defects of mendeleevs periodic table?
- The defects of mendeleevs periodic table are:
- Hydrogen was placed in group IA along with alkali metals, but it could also be placed along with along with halogens in group VIIA.
- Position of isotopes of same elements was different.
- Alkali metals and coinage metals like copper, gold, silver were put in the same group.
-  There was no proper position of lanthanides and actinides.

5. State modern periodic law.
- It states that, the physical and the chemical properties of elements are the periodic function of the atomic number. 

VVI QUESTIONS (ELECTRICITY AND MAGNETISM)

1. Define electric circuit. What is the unit of electricity consumption?
2. Draw a daigram of circuit having 3 bulbs connected in parallel with a cell and switch. Write two advantages of such connection.
3. How are the loads connected in domestic wiring? Give two advantages of this type of connection of loads.
4. Which element is used to make main switch box in a domestic wlectric circuit, why?
5. What is fuse? Why is it connected in a live wire? What is it made up of?
6. Define short circuit.
7. Differentiate between AC and DC.
8. What do you mean by the frequency of electricity is 50 Hz?
9. Relate current, p.d and power with formula.
10.Differentiate between fuse wire and phase wire.
11. Define overloading.
12. Write any two characteristics of a fuse wire.
13.Why is 220v marked in most electrical appliances?
14. Why is MCB better than fuse? What does MCB stands for?
15. Define neutral wire.
16. Calculate the energy consumption of one day when 5 tube lights of 40 watt each are run five hours a day.
17. 10 bulbs of 60 watt each and two heaters of 1500 watt each are used for two hours daily. Find the unit of electricity consumed in 30 days.
18. What is lightening effect of current?
19.What is filament? Which metal is used for filaments? Why?
19. Why is tungsten filament used in elwctric bulb?
20. Differentiate a filament  lamp and a fluorescent lamp.
21. Why is nitrogen and inert gas filled in a filament lamp?
22. Nichrome wire is used as a heating element, why?
23. A fluorescent lamp of 60 watt glows brightly than a filament lamp of same power, why?
24. What does CFL stands for?
25. Define magnetic effect of current. Who discovered it?
26. What is electromagnetic induction? Write its use.
27. Define motor effect and transformer.
28. Differentiate between step up and step down transformer with examples. What is used to laminate their cores?
29. Why is the core of transformer laminated?
30. Differentiate between a generator and an electric motor.
31. On what principle is transformer based?
32.  On what effect of electricity  an electric bell based?
33. What is the principle of dynamo?
34. What is a solenoid?
35. A coil made up of insulated copper wire is connected to a galvanometer. What will happen to the deflection in the galvanometer if this coil is moved towards a stationary bar magnet and then moved away from it? Give reason. Name the phenomenon involved.

VVI QUESTIONS (LIGHT)

1. Write the difference between convex and concave lens.
2. Convex lens and concave lens are called converging and diverging lens respectively, why?
3. What do you mean by "the power of lens is 1 dioptre?
4. Define magnification of lens.
5. Define focus and focal length.
6. Define power of lens and it's unit.
7. If a burning candle is placed at a distance of 4 cm from a convex lens having a focal length of 2 cm, draw a ray  diagram to show the information of the image.
8.practise all ray diagram.
9. In which condition does a convex lens give erect image? Draw a ray diagram.
10. What is focusing of lens?
11. Define defect of vision.
12. Differentiate between myopia and hypermetropia.
13. Give two example of optical instrument.
14. Define near point of an eye.
15. Draw a diagram of eye suffering from myopia and it's corrected image. Also mention the causes and remedies of it.
16. Draw a diagram of eye suffering from hypermetropia and it's corrected image. Also mention the causes and remedies.
17. A man uses lens of +1.5D. Draw a diagram to show defect of his eyes.
18. Difference between eye lens and lens of camera.
19. Define far point. What is it's value for a normal eyes? Write function of ciliary muscle and iris.
20. If the focal length of the lens of the spectacles needed for this eye is 50cm, what will be it's power?

VVI QUESTIONS (HEAT)

1. Define heat with its S.I unit.
2. Write two factors that effect heat.
3. Define 1 calorie and 1 joule heat. Write relation between calorie and heat.
4. Why is there gap in between track of rails?
5. State the principle of thermometer.
6. Which instruments measures heat?
7. Define thermal expansion.
6. Define temperature with it's unit and relation between them.
7. Define thermometer. Why is mercury used as thermometric liquid.
8. Why is alcohol used as thermometric liquid.
9. Differentiate between clinical and laboratory thermometer.
10. Kink is present in clinical thermometer, why?
11. Which thermometer is used in cold region, why?
12. Which thermometer is used to measure the temperature of boiling water.
13. Define specific heat capacity. What is it's value for water?
14. Define and prove heat equation.
15. Write the relation between heat gained and lost by an object in ideal condition.
16. What is the relation between specific heat capacity with heat.
17. Why is water used as cooling agent?
18. Why is water used in hot bags?
19. Why is desert very hot during day and very cold during night?
20. What is normal human body temperature?
21. Well water is warmer during cold days, why?
22. Water kept in earthen pot is cold, why?

VVI QUESTIONS(ENERGY)

1. Differentiate between renewable and non-renewable source of energy with eg.
2. Fossil fuel is known as non-renewable source of energy, why?
3. Sun is called the ultimate source of energy, why?
4. Hydropower is efficient in the context of Nepal, why?
5. What are the necessary condition for nuclear reaction to take placein the sun.
6. Write the mechanism of  solar energy production in sun.
7. Define nuclear fusion and nuclear fission reaction with examples.
8. Define fossil fuel with example.
9. Write the major disadvantage of fossil fuel.
10. Define alternative source of energy with examples.
11. Define energy crisis with it's causes and solution.
12. Define geothermal energy, bio-mass, bio-gas and bio-fuel.
13. Write the name of any two radio active elements.
14. How can geothermal energy be obtained?
15. What is tidal energy?
16. Write the applications of coal and bio-gas.

VVI QUESTIONS (PRESSURE)

1.Define pressure with it's S.I unit.
2. Write the factors that affect pressur.
3. Define one pascal pressure.
4. Prove P=F/A.
5. Wheels of tractor is wider, why?
6. Foundation of buildings are made wider, why?
7. Studs are made on players shoes, why?
8. What is difference between air filled balloon and a hydrogen filled balloon?
9. Turban are kept on head while carrying loads, why?
10. State pascal's law with formula. Write the instrument based on it.
11. What is hydraulic press?Why is liquid used in hydraulic press?
12. Prove that hydraulic machines multiplies force.
13. Define upthrust with it's unit.
14. Write the factors on which upthrust depends.
15. How are density and upthrust related?
16. Differentiate between density and relative density.
17. Why is it easier to pull a bucket of water from the well until it is inside the water but difficult out of water?
18. Weight of an object decreases inside water, why?
19. Ship made up of metal floats but iron nail sinks, why?
20. State Archimede's principle and law of floatation.
21. Name a device based on law of floatation.
22. The bulb of hydrometer is  made heavy, why?
23. Differentiate between immersion of hydrometer in pure and salty water.
24. Define atmospheric pressure with it's value at the sea level.
25. Explain the working of syringe, hand pump, air pump and barometer.

VVI QUESTIONS(GRAVITATION)

1. Define gravity and gravitation.

2. State and prove Newtons universal law of gravitation.

3. Define Universal gravitational constant with its S.I unit.

4. What is the effect of gravity on falling object?

5. Why does tides occur on ocean during new moon day and full moon day?

6. Satellites does not need any energy to revolve around the earth,why?

7. Define acceleration due to gravity with its unit.
8. What do you mean by acceleration due to gravity of the earth is 9.8m/s^2?
9. What is the conclusion of Galileo's feather experiment?
10. Feather and coin fall together on moon, why?
11. People get more hurt while jumping from more height, why?
12. Define mass and weight with S.I unit.
13. Where does the weight of body become maximum in Nepal?
14.Where does the weight of body become maximum on the earth, why?
15. What happens to the weight of an object when taken to moon, why?
16. Differentiate between freefall and weightlessness.
17. Write the condition for freefall.
18. When does weightlessness occur?

ELECTRICITY AND MAGNETISM.

1. Define circuit.
- The path made by connecting the electric source, load, and switch with a conducting wire allows current to pass through it is called circuit.

2. Define open and closed circuit.

- The circuit in which the switch is off or the wire is broken or the fuse is blown off is called open circuit.
- The circuit in which electricity is continuously flowing is called closed circuit.

3. What do you mean by connection of loads?
- The combination of two or more loads in a circuit is called connection of loads. Mainly it is of two types:
parallel and series.

4. What do you mean by domestic electrification?
- The electric circuit which is connected in places like homes, industries, factories etc. Is called domestic circuit. Generally, Alternating current (AC) is used.

5. Define DC and AC with example.
- The current which does not change the polarity and magnitude is called direct current (DC). For example,current obtained from a battery, dry cell, DC generator etc.
- The current which changes polarity and magnitude continously is calledalternating current(AC). For example, current obtained from a dynamo, generator etc.

6. What are thee points to be remembered during a house wiring?
- The points to be remembered during house wiring are:
a. Switch and fuse should always be connected in phase or live wire.
b. Fuse with suitable power should be used.
c. Wiring should not be done in moist and damp places.
d. The lines for light and power sockets should be seperate.

7. What are the types of electric wires?
- The types of wire are as follows:
a. Live wire or phase wire: The wire which conducts current from a source of electricity to load is known as live wire or phase wire. Its color is red or brown.

b. Neutral wire: The wire which conducts electricity from electric appliances to the source of electricity is called a neutral wire. Its color is black or blue.

c. Earthing wire: The wire connecting electric appliances to the earth is called earthing wire. It carries leakage of current from the outer surface of electrical appliances to the earth. Its color is green or yellow.

LIGHT

LIGHT
1. Define light.
- Light is defined as a form of energy which gives us the sensation of warmth.

2. Define lens with it's types.
- A transparent refractive medium bounded by two curved surfaces is called lens. It's types are:
a. Concave lens (Diverging lens)- A lens which is thinner at the middle and thicker at the edge is called concave lens.
b. Convex lens (Converging lens)- A lens which is thicker at the middle and thinner at the edge is called convex lens.

3. Define center of curvature.
- The center of the sphere of which the lens is formed is called center of curvature.

4. Define principal axis and optical center.
- The imaginary line joining the two centre of curvature of a lens is called principal axis.
- The mid-point of two centre of curvature is called optical centre.

5. Define principal focus and focal length.
- The point through which the parallel rays of light passes or appears to pass after refrating through the lens is called principal focus.
- The distance between optical center and focus is called focal length.

6. Define focusing. 
- The process of adjusting the distance between the lens and screen in order to produce a clear and distinct image is called focusing.

7. Define power of lens with its unit.
- The converging or diverging capacity of a lens is called the power of a lens. Its S.I unit is dioptre(D). And mathematically,
                                                    power= 1/focal length

8. Define Magnification.
- The ratio of the length or height of the image to the length or height of the object is called magnification. It does not have any unit. Mathematically,
                                                  Magnification(M)= Length of image(I)/Length of object(O)
                                                                               = Distance of image (V)/Distance of object(U)
9. Define optical instrument and Hand lens.
- Instruments which produce an image of an object by using a lens are called optical instruments.
- A hand lens is a simple microscope with a convex lens and handle.

10. Define camera.
- It is an optical instrument having  a convex lens which is used to take photographs of the objects.

HEAT

HEAT
1. Define heat or heat energy with its unit.
-Heat or heat energy is defined as the sum of the kinetic energy possessed by the molecules of an object. It's S.I unit is Joule and C.G.S. unit is calorie.

2. Write the factors on which the heat depends.
- The factors on which the heat depends are:
a. The number of atoms of matter.
b. The average Kinetic energy of the molecules.

3. Define one calorie and one joule heat .
- The quantity of heat required to raise the temperature of one gram of pure water by  one kelvin or one degree Celsius is called one calorie.
- The quantity of heat required to raise the temperature of one kilogram of pure water by one kelvin or one degree Celsius is called one joule heat.

4. Write the effects of heat. 
- The effects of heat are:
a. Heat causes change in volume.
b. Heat causes change in state.
c. Heat causes change in solubility.
d. Heat causes change in temperature.

5.  Define temperature with its unit.
- Temperature is defined as the average kinetic energy of the molecules of an object.

or

- Temperature is defined as the measure of degree of hotness or coldness of the body.

It's S.I. unit is kelvin, Fahrenheit and centigrade.

6. What are the effects of heat?
- The effects of heat are as follows:
- Heat causes change in volume.
- Heat causes change in temperature.
- Heat causes change in the solubility.
- Heat causes change in physical state.

7. Define temperature with its SI unit. 
- It is defined as the average kinetic energy of the molecules. Its SI unit is kelvin.

8. State the principle of thermometer.
- It states that substance expand in heating and contracts on cooling.

ENERGY

1. Define energy with it's unit.
- The capacity of doing work is called energy. It's unit is Joule and CGS unit is calorie.

2. State law of conservation of energy.
- Law of conservation of energy states that, energy can neither be created nor be destroyed but it can be transformed from one form to another.''

3. Define primary sources of energy with it's types.
- Primary sources of energy can be defined as the source of energy which are utilize in the form of natural availability. It's types are:
a. Non-renewable sources of energy: The sources of energy that cannot be renewed time and again and take a very long time to form once they finish are called non-renewable sources of energy. For example, coal, mineral oil, natural gas etc.
b. Renewable sources of energy: The sources of energy that can be renewed time and again and do not take a very long time to form once they finish are called renewable sources of energy. For example, solar energy, bio mass, hydro electricity etc.

4. Why is the sun called ultimate source of energy?
- The sun is called the ultimate sources of energy because it is the prime or major source of energy and solar energy is stored in all sources of energy, directly or indirectly.

5. What are the conditions required for nuclear reaction in the sun?
- The necessary conditions required for nuclear energy in the sun are:
a. Presence of high temperature in the sun.
b. Presence of abundant amount of  hydrogen gas in the sun.
c. Presence of high pressure in the sun.

6. What are the types of nuclear reactions?
- The types of reactions are as follows:
a. Nuclear fission reaction: The process in which a heavy nucleus of a radioactive element breaks down into two or more lighter nuclei is called a nuclear fission reactions. It can be controlled.
b. Nuclear fusion reaction: The process in which two or more than two lighter nuclei fuse together together to form a single heavy nucleus  is called a nuclear fusion reaction. It cannot be controlled.

7. Define nuclear fuel.
- The radioactive material which is used in the process of nuclear reaction is called nuclear fuel.

8. What are the three isotopes of hydrogen?
- The three isotopes of hydrogen are Protium, Deuterium(Heavy hydrogen) and Tritium(isotope of hydrogen).

9. Define fossil fuels.
- The fuels obtained from the dead remains of plants and animals that were buried in the earth's crust millions of year ago are known as fossil fuel.

10. Define coal.
- The hard and black rock which contains carbon is called coal.

11. What are the benefits of coal and mineral oil?
-  The benefits of coal and mineral oils are as follows:
a. Coal and mineral oil have low cost and can easily be transported.
b. Coal and mineral oil are more abundant in comparison to other types of fuels.
c. They give abundant heat after combustion.

PRESSURE

PRESSURE
1. What is pressure? Write its S.I. unit.
-Pressure is a perpendicular force acting on per unit area. It's S.I  unit is pascal.

2. Define 1 pascal pressure.
- One pascal pressure is defined as one newton of force applied on the surface area of  one meter square.

3. All cutting instrument has sharp edges, why?
- We know,  P=F/A
which means pressure is inversely proportional to the  surface area if force is kept constant.So, the sharp edges has small surface area and are capable of exerting more pressure due to it which makes cutting easier. Hence, they have sharp edges.

4. Define liquid pressure and derive p=hdg.
- The force exerted by liquid on per unit area of the wall of the container is called liquid pressure.

5. List the factors on which liquid pressure depends.
-The factor on which liquid pressure depends are:
a. Depth of the liquid. (h)
b. Density of the liquid.(d)
c. Acceleration due to gravity.(g)

6. List the laws of liquid pressure.
- The laws of liquid pressure are:
a. Liquid find it's own level.
b. Pressure applied on an enclosed liquid transmits equally in all direction.
c. Liquid pressure is directly proportional to the depth of the liquid.
d. Liquid pressure depends on its density

7. Why are dams made wider at the base?
- Since, P=hdg. It is clear that more the depth of the liquid more will be the pressure. Hence, to withstand the enormous amount of pressure the dams are made wider at the base.
 # SIMILAR ANS TO THE FOLLOWING QUESTION.
*Deep sea divers use swim suit, why?
* A bucket at ground floor fills faster than at the top floor, why?

8. State pascals law and instrument based on it.
- It state that"the pressure exerted in any part of  enclosed fluid transmits equally and perpendicularly to all the other part of the fluid."
Instruments based on it are:
Hydraulic lift, Hydraulic press, Hydraulic brakes e.t.c.

9. Explain the working principle of hydraulic machines.
- Let F1 and F2 be the force applied in small and big piston respectively and A1 and A2 be their respective surface area. Hence, we know from pascals law ,

Since, A2 is greater than A1, F2 will be greater than F1. It shows that the force is multiplied.

10. What are the reason for using liquid in a hydraulic lift?

- The reasons for using liquid in a hydraulic lift are:

a. Liquid transmits pressure equally in all direction.

b. Liquid's volume cannot be changed by compressing.

11. Define upthrust or buoyancy with it's unit. In which direction does it act?

- Upthrust is defined as the resultant upward force experienced by an object when immersed partially or wholly. It's S.I unit is Newton. It acts in the direction opposite to the direction of gravity (Upward).

12. Write the factors on which upthrust depends.

- Since, U= vdg. It is clear that upthrust depends on following factors:

a. Volume of displaced liquid (v).

b. Density of the liquid(d).

c. Acceleration due to gravity(g).

12. Write the relationship between density of liquid  and upthrust.
- The upthrust is directly proportional to the density of the liquid.

Note- Therefore salty water provides greater upthrust than pure water and egg float on salty water.

13. Define density and relative density with its unit.
- The total amount of mass present per unit volume is called density. It's unit is kg per meter cube.
Mathematically, d=m/v.
- Relative density is defined as the ratio of density of the substance to that of density of water at 4°c.It has no unit.
Mathematically,
R.D=density of substance/density of water at 4°c.

14.  State Archimedes principle.
-Archimedes principle states that,"when an object is wholly or partially immersed into a liquid, it experiences an upthrust which is equal to the weight of the displaced liquid".

15. Where does an object has less weight in air  or in liquid?
- An object has less weight in liquid because liquid exerts more upthrust than air.

16. State law of floatation.
- Law of floatation states that," Every floating object displaces liquid equal to its own weight".

Note-  Ship floats on water because it displaces liquid equal to it's own weight and due to its hollow body, it's density is less than that of water.
Iron nail sinks in water because it cannot displace liquid equal to its own weight and has more density than water.

17. What are the application of law of floatation?
- The application of law of floatation are:
a. To make a hydrometer.
b. To make a ship.

18.  What is hydrometer? Give an example.
- A hydrometer is a device which is used to measure the density and relative density of various liquid and it is based on law of floatation. For example- lactometer is used to measure the purity (density)of the milk.

19. Define atmosphere.
- The mixture of different gases, dust particles, sand, water vapour etc. Which is present around the earth's surface is call atmosphere.

20. Define atmospheric pressure and it's value at the sea level.
- The force applied by the mixture of air on a unit surface area of the earth is called atmospheric pressure.
It's value at sea level is 760 mm of Hg or 10^6 pascal.

21. What are the application of atmospheric pressure?
- The application of atmospheric pressure are-
 We cal fill ink in a fountain  pen, medicine in a syringe, to draw water using water pump etc.

22. What is a Barometer? Write its working.
-It is the instrument use to measure the atmospheric pressure.
Working- Inside a barometer, there is some vacuum just above the mercury level which is called Toricellian vacuum. When atmospheric pressure decreases, the level of mercury in a barometer decreases and when the atmospheric pressure increases, the level of mercury increases.

23. Define syringe and it's working.
- A syringe is a medical instrument which is used to take out blood from our body or inject medicine.

Working: A syringe consist of a needle, nozzle, piston and a cylindrical body. When a piston is pulled a vacuum is created inside the body and the medicine from a bottle enters it, when the piston is pushed the pressure inside the syringe becomes more than that of our body and hence the medicine enters our body through needle.

24. Define air pump with working.
- It is an instrument which is used to fill air in the tubes of tyres .

Working- It consist of a nozzle,cylindrical body and a piston. When the piston is pulled the air enters the cylindrical body as the atmospheric pressure is more than that of pressure inside the pump. When the piston is pulled the pressure inside the pump becomes more than the pressure of tube and hence air enters the tube.

Note- Pressure gauge measures the pressure in the tubes of Tyre.

25. Define hand pump and it's working.
- It is an instrument used to draw the water from under ground.
 
Working: It consist of move able valve and barrel valve,handle, cylindrical body, outlet and a piston.
There are two processes;
a. Upstroke- When the handle is pushed, the piston comes up and vacuum is created between barrel valve and move able valve. Due to low pressure move able valve gets closed and  water rises through barrel valve. Hence, pushing down of handle to rise up the piston is called upstroke.
b. Down stroke- When handle is pulled, the piston moves down and move able valve opens and barrel valve closes. Since both valves comes closer the pressure between them increases and the water rises up through movable valve. So, pulling up of the handle to push down the piston is called down stroke.

26. Why does the helium filled balloon rises and then halts?
- The density of helium is less than air. So, due to the upthrust of air it rises up. When the density of air equals to density of helium it halts.

27. Which instrument measures the blood pressure of human body?
- Sphygmomanometer is the instrument used to measure the blood pressure of human body.

GRAVITATION.

GRAVITATION

1. State heliocentric and geocentric theory.

- Heliocentric theory states that “ the sun is at the center of the universe and all other planets and satellites revolve around the sun in their own axis” and geocentric theory states that “the earth is at the centre of the universe and all the heavenly bodies like the sun, the moon etc. revolve around the earth”.

2. Define gravitation.

- The force of attraction between any two objects of the universe due to their masses is called gravitation.

3. When the apple falls, does it attract the earth?

- Yes when the apple falls it attracts the earth. However, due to less mass the apple cannot create the noticeable acceleration like earth does to the apple. Hence, we see apple moving towards earth but not vice versa.

4. Define Newton’s universal law of gravitation.

- It states that “the gravitational force acting on any objects in the universe is directly proportional to their masses and inversely proportional to the square of the distance between their centers.”

4. Define G and illustrate it’s properties.

- Newtons universal gravitational constant (G) is defined as the gravitational force between any two  objects having unit masses and separated by unit distance. Its properties are:

   1. The value of G is not affected by  temperature, pressure and time.

   2. It is independent of direction of gravitational force.

   3. It is independent to the nature of the masses.

Therefore, it is constant.

5. What are the consequences of gravitational force.

- The consequences of the gravitational force are:

   1. Earth holds the atmosphere.

   2. Due to mutual gravitational forces between the sun, the moon and the earth, the tides are formed on the oceans.       

   3. It is responsible for rainfall, snowfall etc.

   4. The object thrown upward falls down.

6. Define gravity or weight with it's S.I unit.
- The force of attraction exerted by the earth on a body is called gravity or weight. It's S.I unit is Newton. Mathematically,     W=m x g

7. Define Mass.
- The total amount of matter contained in a body is called mass. It's S.I unit is kg.

8. Define acceleration due to gravity with it's unit. Derive an expression for it.
- The acceleration produced in a freely falling body due to earths gravity is called acceleration due to gravity. Let F be the gravitational force, M be the mass of the earth and R be it's radius.

9. Write the factors on which acceleration due to gravity depends.

- Acceleration due to gravity depends upon following factors:

1. Directly proportional to the mass of the earth.

2. Inversely proportional to the square of the radius of the earth.

NOTE- It is independent to the mass of the object lying on the earth's surface.

10. What are the effects of gravity?
-  The effects of gravity are:
1. River flows due to gravity.
2. Acceleration is produced in falling object.
3. The earth is covered by atmosphere.
4. Objects thrown upward return to the earth's surface.

11.  Why is it difficult to lift larger stone?
- Since,  weight= mass x acceleration due to gravity, we know larger stone has more mass which means it has more weight. Hence, it is difficult to lift larger stone.

12.  Explain Guinea and Feather experiment.
- A Guinea and feather are placed in a long and wide glass tube, when they are at bottom the tube is inverted. In this case the coin falls faster than feather but when a vacuum is created in a glass tube and is inverted, the coin and feather falls simultaneously.
Conclusion- The acceleration due to gravity is independent of masses in absence of air resistance.                           
                                                   

13. What is the value of g at poles and equator of the earth?

- The value of g at poles and equator are 9.83 m/s/s and 9.78 m/s/s respectively. (m/s/s=meter per second square)

14.  The value of g is more at pole than in equator, why?

- We know, g=GM/R^2

As earth is bulged out at the equator and flat at poles, radius of equator is greater than radius of pole and from above formula it is clear that more the value of radius less will be the value of g. Hence, g is more at pole than in equator.

15. Define gravitational field and gravitational field intensity.

- Gravitational field is defined as the area around the heavenly body up to which its gravitational force can be felt.

- Gravitational field intensity is defined as the force experienced by a unit mass kept at any point in gravitational field. It's S.I unit is N/Kg.

16. Define free fall and weightlessness.

- If an object falls freely only under the effect of gravity neglecting air resistance, the body is said to be in a free fall. For example, object falling on the surface of the moon.

- Weightlessness is defined as the condition in which effective weight of a body becomes zero.For example, When a person falls freely in a lift.

17. What are the condition for weightlessness.

-  The conditions for weightlessness are:

a. In free fall.

b. At the center of the earth.

c. At null point outside Gravitational field.

d. In satellite orbiting round the heavenly body.

18.  The weight of the body is more in the terai than in the Himalayan region, why?

-  We know, weight= mass x g  

and,                                                    

Clearly the g is inversely proportional to the square of the  distance from the center of the earth, as terai has less distance from the center of the earth , g is more at terai and hence weight of the body is more in the terai than in Himalayan region.

19. The value of 'g' is zero at the center of the earth, why?

- We know, acceleration due to gravity at the center of the earth is given by g=(1-d/R).g and the value of d=R at the center of the earth so the value of g becomes zero.

20.  What is the difference between the falling of parachute on the earth and the moon?

- In earth, due to the presence of air resistance the parachute falls slowly with constant velocity called  terminal velocity (WHICH MEANS g=0 m/s/s) but due to absence of air resistance on the moon the falling of parachute is a free fall.

21. Can masslessness be called weightlessness, why?

- No, because mass is constant quantity where as weight varies from place to place and the body experience weightlessness only due to zero reactional force which may be due to zero gravity or free fall.

22. Moon doesn't have atmosphere, why?

- Due to it's insufficient gravity which produces acceleration of only 1.67 m/s/s, the moon cannot retain the atmosphere and hence, it is atmosphere less.