Question

UNIT 6 WORK AND ENERGY 7. Describe the processes by which energy is converted from one form to another with reference to fossil fuel energy, hydroelectric generation, solar energy, nuclear energy, geothermal energy, wind energy and biomass energy. 8. Describe the process of electricity generation by drawing a block diagram of the process from fossil fuel input to electricity output. 9. Define power. What is the relation of its SI unit with horse power? 10. What is efficiency. Why is it important for cars or electronic devices to be designed with high efficiency? Why efficiency of machines can never be unity or \( 100 \% \) ? 11. Explain by drawing energy flow diagrams through steady state systems such as Filament lamp, a power station, a vehicle traveling at a constant speed on a level road. HUMERICAL RESPONSE QUESTIONS QiV. Solve the following. 1. Calculate the work done in pushing a box with 150 N through distance of 5 m . (Ans. 750 J ) 2. Aboy weighing 75 N jumps up and gains 300 J of gravitational potential energy. Find the height to which the boy will rise. (Ans. 4 m ) 3. A 5 kg steel ball is dropped from the top of a 12 m high tower. What is kinetic energy of the ball on hitting the ground? With what velocity will it hit the ground? (Neglect air resistance). (Ans. 588 J and \( 15.3 \mathrm{~m} / \mathrm{s} \) ) 4. A 2.0 kg rock is dropped from 20 m tall building. What is the Kinetic and gravitational potential energy when the rock has fallen 15 m . (Ans. \( E_{k}=294 \mathrm{~J} \) and \( E_{p, \text { grav }}=98 \mathrm{~J} \) ) 5. A rocket with a mass of 800 g is launched vertically upward with an initial speed of \( 30 \mathrm{~m} / \mathrm{s} \). (a) Assuming no air resistance, calculate the maximum height the rocket would reach. (b) If, due to air friction, the rocket only rises to 25 m , determine the work done against air resistance. (Ans. (a) 45.92 m , (b) -164 J ) 6. A 2 hp electric motor gives energy to a system that lifts a load of 100 kg to height of 10 m in 1.5 s. Calculate (a) Input (work done by motor on system) (b) Output (load lifted by system) and (c) Efficiency of the system. (Ans. (a) 2238 J , (b) 980 J and (c) \( 22.8 \% \) What horsepower (hp) is required to pump up 2500 kg of water to 100 m height in 5 minutes? (Ans. 95 hp ) 164

          UNIT 6 WORK AND ENERGY
7. Describe the processes by which energy is converted from one form to another with reference to fossil fuel energy, hydroelectric generation, solar energy, nuclear energy, geothermal energy, wind energy and biomass energy.
8. Describe the process of electricity generation by drawing a block diagram of the process from fossil fuel input to electricity output.
9. Define power. What is the relation of its SI unit with horse power?
10. What is efficiency. Why is it important for cars or electronic devices to be designed with high efficiency? Why efficiency of machines can never be unity or \( 100 \% \) ?
11. Explain by drawing energy flow diagrams through steady state systems such as Filament lamp, a power station, a vehicle traveling at a constant speed on a level road.
HUMERICAL RESPONSE QUESTIONS
QiV. Solve the following.
1. Calculate the work done in pushing a box with 150 N through distance of 5 m .
(Ans. 750 J )
2. Aboy weighing 75 N jumps up and gains 300 J of gravitational potential energy. Find the height to which the boy will rise.
(Ans. 4 m )
3. A 5 kg steel ball is dropped from the top of a 12 m high tower. What is kinetic energy of the ball on hitting the ground? With what velocity will it hit the ground? (Neglect air resistance).
(Ans. 588 J and \( 15.3 \mathrm{~m} / \mathrm{s} \) )
4. A 2.0 kg rock is dropped from 20 m tall building. What is the Kinetic and gravitational potential energy when the rock has fallen 15 m .
(Ans. \( E_{k}=294 \mathrm{~J} \) and \( E_{p, \text { grav }}=98 \mathrm{~J} \) )
5. A rocket with a mass of 800 g is launched vertically upward with an initial speed of \( 30 \mathrm{~m} / \mathrm{s} \). (a) Assuming no air resistance, calculate the maximum height the rocket would reach. (b) If, due to air friction, the rocket only rises to 25 m , determine the work done against air resistance.
(Ans. (a) 45.92 m , (b) -164 J )
6. A 2 hp electric motor gives energy to a system that lifts a load of 100 kg to height of 10 m in 1.5
s. Calculate (a) Input (work done by motor on system) (b) Output (load lifted by system) and (c) Efficiency of the system.
(Ans. (a) 2238 J ,
(b) 980 J and
(c) \( 22.8 \% \)

What horsepower (hp) is required to pump up 2500 kg of water to 100 m height in 5 minutes?
(Ans. 95 hp )
164

UNIT 6 WORK AND ENERGY
7. Describe the processes by which energy is converted from one form to another with reference to fossil fuel energy, hydroelectric generation, solar energy, nuclear energy, geothermal energy, wind energy and biomass energy.
8. Describe the process of electricity generation by drawing a block diagram of the process from fossil fuel input to electricity output.
9. Define power. What is the relation of its SI unit with horse power?
10. What is efficiency. Why is it important for cars or electronic devices to be designed with high efficiency? Why efficiency of machines can never be unity or 100 % ?
11. Explain by drawing energy flow diagrams through steady state systems such as Filament lamp, a power station, a vehicle traveling at a constant speed on a level road.
HUMERICAL RESPONSE QUESTIONS
QiV. Solve the following.
1. Calculate the work done in pushing a box with 150 N through distance of 5 m .
(Ans. 750 J )
2. Aboy weighing 75 N jumps up and gains 300 J of gravitational potential energy. Find the height to which the boy will rise.
(Ans. 4 m )
3. A 5 kg steel ball is dropped from the top of a 12 m high tower. What is kinetic energy of the ball on hitting the ground? With what velocity will it hit the ground? (Neglect air resistance).
(Ans. 588 J and 15.3 m / s )
4. A 2.0 kg rock is dropped from 20 m tall building. What is the Kinetic and gravitational potential energy when the rock has fallen 15 m .
(Ans. Ek=294 J and Ep, grav =98 J )
5. A rocket with a mass of 800 g is launched vertically upward with an initial speed of 30 m / s. (a) Assuming no air resistance, calculate the maximum height the rocket would reach. (b) If, due to air friction, the rocket only rises to 25 m , determine the work done against air resistance.
(Ans. (a) 45.92 m , (b) -164 J )
6. A 2 hp electric motor gives energy to a system that lifts a load of 100 kg to height of 10 m in 1.5
s. Calculate (a) Input (work done by motor on system) (b) Output (load lifted by system) and (c) Efficiency of the system.
(Ans. (a) 2238 J ,
(b) 980 J and
(c) 22.8 %

What horsepower (hp) is required to pump up 2500 kg of water to 100 m height in 5 minutes?
(Ans. 95 hp )
164

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