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Class 9 Physics Transfer of Heat 2. How much work is needed to move horizontally a body 20 \mathrm{~m} by a force of 30 \mathrm{~N} the angle between the body and the horizontal surface is 60^{\circ} ?


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2. How much work is needed to move horizontally a body 20 \mathrm{~m} by a force of 30 \mathrm{~N} the angle between the body and the horizontal surface is 60^{\circ} ?

b) The energy of 600 \mathrm{~J} dissipated by a bulb in 50 minutes. Find the power of the bulb.
b) The energy of  600 \mathrm{~J}  dissipated by a bulb in 50 minutes. Find the power of the bulb.

b) The energy of 600 \mathrm{~J} dissipated by a bulb in 50 minutes. Find the power of the bulb.

4. A body of mass 1 \mathrm{~kg} is lifted through a height of 1 \mathrm{~m} . The energy possessed in the body will be (consider g=10 \mathrm{~ms}^{-2} )a) 1 \mathrm{~J} b) 10 Joulec) 100 Jouled) 1000 Joule
4. A body of mass  1 \mathrm{~kg}  is lifted through a height of  1 \mathrm{~m} . The energy possessed in the body will be (consider  g=10 \mathrm{~ms}^{-2}  )a)  1 \mathrm{~J} b) 10 Joulec) 100 Jouled) 1000 Joule

4. A body of mass 1 \mathrm{~kg} is lifted through a height of 1 \mathrm{~m} . The energy possessed in the body will be (consider g=10 \mathrm{~ms}^{-2} )a) 1 \mathrm{~J} b) 10 Joulec) 100 Jouled) 1000 Joule

10. Write notes on Tidal energy and Geothermal energy.
10. Write notes on Tidal energy and Geothermal energy.

10. Write notes on Tidal energy and Geothermal energy.

9.6 Why transfer of heat in fluids takes place by convection?
 9.6 Why transfer of heat in fluids takes place by convection?

9.6 Why transfer of heat in fluids takes place by convection?

9.2 Why metals are good conductors of heat?
9.2 Why metals are good conductors of heat?

9.2 Why metals are good conductors of heat?

9.3 Explain why:(a) a metal feels colder to touch than wood kept in a cold place?
9.3 Explain why:(a) a metal feels colder to touch than wood kept in a cold place?

9.3 Explain why:(a) a metal feels colder to touch than wood kept in a cold place?

10 . is not a renewable source of energy.a) Solar energyb) Coalc) Wind energyd) Geothermal energy
 10 .  is not a renewable source of energy.a) Solar energyb) Coalc) Wind energyd) Geothermal energy

10 . is not a renewable source of energy.a) Solar energyb) Coalc) Wind energyd) Geothermal energy

1. a) Definework?
1. a) Definework?

1. a) Definework?

9.7 What is meant by convection current?
9.7 What is meant by convection current?

9.7 What is meant by convection current?

b) Write the names of any one device that can convert solar energy into heat energy.
b) Write the names of any one device that can convert solar energy into heat energy.

b) Write the names of any one device that can convert solar energy into heat energy.

9.12 Explain the impact of greenhouse effect in global warming.
9.12 Explain the impact of greenhouse effect in global warming.

9.12 Explain the impact of greenhouse effect in global warming.

16. Make a table of renewable and non-renewable energy sources from the following:Uranium Solar Coal Wind Natural gas Tidal Biomass Hydroelectricity.
16. Make a table of renewable and non-renewable energy sources from the following:Uranium Solar Coal Wind Natural gas Tidal Biomass Hydroelectricity.

16. Make a table of renewable and non-renewable energy sources from the following:Uranium Solar Coal Wind Natural gas Tidal Biomass Hydroelectricity.

22 . a) Convert 20 w att into horse power.
 22 . a) Convert  20 w  att into horse power.

22 . a) Convert 20 w att into horse power.

1. If force of 6 \mathrm{~N} displaces an object 2 \mathrm{~m} in the direction of force then work done will bea) 0b) 12 Joulec) 3 Jouled) Both band c
1. If force of  6 \mathrm{~N}  displaces an object  2 \mathrm{~m}  in the direction of force then work done will bea) 0b) 12 Joulec) 3 Jouled) Both band  c

1. If force of 6 \mathrm{~N} displaces an object 2 \mathrm{~m} in the direction of force then work done will bea) 0b) 12 Joulec) 3 Jouled) Both band c

c) Write the names of any two devices that can convert solar energy into electrical energy.
c) Write the names of any two devices that can convert solar energy into electrical energy.

c) Write the names of any two devices that can convert solar energy into electrical energy.

Worked Example 3A ball of mass 50 gram is raised to a height of 7 \mathrm{~m} from the ground. Calculate its gravitational potential energy?
Worked Example 3A ball of mass 50 gram is raised to a height of  7 \mathrm{~m}  from the ground. Calculate its gravitational potential energy?

Worked Example 3A ball of mass 50 gram is raised to a height of 7 \mathrm{~m} from the ground. Calculate its gravitational potential energy?

20. Which machine is more efficient machine "A" which has an output of 200 \mathrm{~J} after consuming 400 \mathrm{~J} of energy or machine " \mathrm{B}^{\prime \prime} which has an output of 300 \mathrm{~J} after consuming 450 \mathrm{~J} of energy?
20. Which machine is more efficient machine "A" which has an output of  200 \mathrm{~J}  after consuming  400 \mathrm{~J}  of energy or machine "  \mathrm{B}^{\prime \prime}  which has an output of  300 \mathrm{~J}  after consuming  450 \mathrm{~J}  of energy?

20. Which machine is more efficient machine "A" which has an output of 200 \mathrm{~J} after consuming 400 \mathrm{~J} of energy or machine " \mathrm{B}^{\prime \prime} which has an output of 300 \mathrm{~J} after consuming 450 \mathrm{~J} of energy?

iii. Metals are good conductor of heat due to the:(a) free electrons(b) big size of their molecules(c) small size of their molecules(d) rapid vibrations of their atoms
iii. Metals are good conductor of heat due to the:(a) free electrons(b) big size of their molecules(c) small size of their molecules(d) rapid vibrations of their atoms

iii. Metals are good conductor of heat due to the:(a) free electrons(b) big size of their molecules(c) small size of their molecules(d) rapid vibrations of their atoms

9.2 How much heat is lost in an hour through a glass window measuring 2.0 \mathrm{~m} by 2.5 \mathrm{~m} when inside temperature is 25^{\circ} \mathrm{C} and that of outside is 5^{\circ} \mathrm{C} the thickness of glass is 0.8 \mathrm{~cm} and the value of k for glass is 0.8 \mathrm{Wm}^{-1} \mathrm{~K}^{-1} ?
9.2 How much heat is lost in an hour through a glass window measuring  2.0 \mathrm{~m}  by  2.5 \mathrm{~m}  when inside temperature is  25^{\circ} \mathrm{C}  and that of outside is  5^{\circ} \mathrm{C}  the thickness of glass is  0.8 \mathrm{~cm}  and the value of  k  for glass is  0.8 \mathrm{Wm}^{-1} \mathrm{~K}^{-1} ?
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9.2 How much heat is lost in an hour through a glass window measuring 2.0 \mathrm{~m} by 2.5 \mathrm{~m} when inside temperature is 25^{\circ} \mathrm{C} and that of outside is 5^{\circ} \mathrm{C} the thickness of glass is 0.8 \mathrm{~cm} and the value of k for glass is 0.8 \mathrm{Wm}^{-1} \mathrm{~K}^{-1} ?

13. Write a note on renewable energy sources?
13. Write a note on renewable energy sources?
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13. Write a note on renewable energy sources?

19. If the efficiency of a machine is 70 \% and its output is 100 \mathrm{~J} then calculate its input.
19. If the efficiency of a machine is  70 \%  and its output is  100 \mathrm{~J}  then calculate its input.
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19. If the efficiency of a machine is 70 \% and its output is 100 \mathrm{~J} then calculate its input.

18. Write a note on efficiency.
18. Write a note on efficiency.
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18. Write a note on efficiency.

Worked Example 2A ball of mass 400 gram strikes the wall of velocity 4 \mathrm{~m} / \mathrm{sec} . How much is the kinetic energy of the ball at the time it strikes the wall?
Worked Example 2A ball of mass 400 gram strikes the wall of velocity  4 \mathrm{~m} / \mathrm{sec} . How much is the kinetic energy of the ball at the time it strikes the wall?
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Worked Example 2A ball of mass 400 gram strikes the wall of velocity 4 \mathrm{~m} / \mathrm{sec} . How much is the kinetic energy of the ball at the time it strikes the wall?

9.11 What is greenhouse effect?
 9.11 What is greenhouse effect?
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9.11 What is greenhouse effect?

v. Convection of heat is the process of heat transfer due to the:(a) random motion of molecules(b) downward movement of molecules(c) upward movement of molecules(d) free movement of molecules
v. Convection of heat is the process of heat transfer due to the:(a) random motion of molecules(b) downward movement of molecules(c) upward movement of molecules(d) free movement of molecules
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v. Convection of heat is the process of heat transfer due to the:(a) random motion of molecules(b) downward movement of molecules(c) upward movement of molecules(d) free movement of molecules

ix. Which of the following is a good radiator of heat?(a) a shining silvered surface(b) a dull black surface(c) a white surface(d) green coloured surface
ix. Which of the following is a good radiator of heat?(a) a shining silvered surface(b) a dull black surface(c) a white surface(d) green coloured surface
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ix. Which of the following is a good radiator of heat?(a) a shining silvered surface(b) a dull black surface(c) a white surface(d) green coloured surface

vii. Rooms are heated using gas heaters by(a) Conduction only(b) Convection and radiation(c) Radiation only(d) Convection only
vii. Rooms are heated using gas heaters by(a) Conduction only(b) Convection and radiation(c) Radiation only(d) Convection only
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vii. Rooms are heated using gas heaters by(a) Conduction only(b) Convection and radiation(c) Radiation only(d) Convection only

8. a) If LED screen of mass 10 \mathrm{~kg} is lifted up and kept it on a cupboard of height 2 \mathrm{~m} . Calculate the potential energy stored in the LED screen.
8. a) If LED screen of mass  10 \mathrm{~kg}  is lifted up and kept it on a cupboard of height  2 \mathrm{~m} . Calculate the potential energy stored in the LED screen.
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8. a) If LED screen of mass 10 \mathrm{~kg} is lifted up and kept it on a cupboard of height 2 \mathrm{~m} . Calculate the potential energy stored in the LED screen.

2. How much work is needed to move horizontally a body 20 \mathrm{~m} by a force of 30 \mathrm{~N} the angle between the body and the horizontal surface is 60^{\circ} ?
2. How much work is needed to move horizontally a body  20 \mathrm{~m}  by a force of  30 \mathrm{~N}  the angle between the body and the horizontal surface is  60^{\circ}  ?
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2. How much work is needed to move horizontally a body 20 \mathrm{~m} by a force of 30 \mathrm{~N} the angle between the body and the horizontal surface is 60^{\circ} ?

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