Section A – Multiple Choice Questions (20 Qs)
Q1. Work done is said to be zero when:
a) Force is applied and displacement is zero
b) Displacement is applied and force is zero
c) Force and displacement are perpendicular
d) All of the above
Q2. SI unit of work is:
a) Joule
b) Watt
c) Newton
d) Erg
Q3. If a body of mass 10 kg is raised to a height of 2 m, the work done is:
a) 20 J
b) 200 J
c) 400 J
d) 100 J
Q4. Energy possessed by a body due to motion is called:
a) Potential energy
b) Kinetic energy
c) Heat energy
d) Chemical energy
Q5. When a body falls freely, the decrease in potential energy is equal to:
a) Increase in kinetic energy
b) Loss in momentum
c) Decrease in mass
d) Loss in velocity
Q6. Work done is negative when:
a) Force is opposite to displacement
b) Force is along displacement
c) Displacement is zero
d) Force is zero
Q7. 1 kWh =
a) 3600 J
b) 36,000 J
c) 3.6 × 10⁶ J
d) 360 J
Q8. The commercial unit of energy is:
a) Watt
b) Kilowatt-hour
c) Joule
d) Newton
Q9. A 1 HP engine is equal to:
a) 736 W
b) 746 W
c) 756 W
d) 1000 W
Q10. The work done on a body is positive if:
a) Angle between force and displacement is 90°
b) Angle between force and displacement is 0°
c) Angle between force and displacement is 180°
d) Force is perpendicular to displacement
Q11. The work done against gravity in moving a 5 kg body through 10 m vertically is:
a) 50 J
b) 500 J
c) 100 J
d) 5 J
Q12. Potential energy is given by:
a) m × g × v
b) m × g × h
c) ½ mv²
d) F × v
Q13. The capacity to do work is called:
a) Displacement
b) Energy
c) Force
d) Power
Q14. Work done per unit time is:
a) Energy
b) Power
c) Force
d) Potential energy
Q15. If velocity of a body is doubled, kinetic energy becomes:
a) Double
b) Four times
c) Half
d) Same
Q16. Unit of power is:
a) Joule
b) Watt
c) Newton
d) Erg
Q17. An electric bulb of 100 W consumes how much energy in 1 hour?
a) 100 J
b) 1000 J
c) 360,000 J
d) 36,000 J
Q18. Which of the following is NOT a form of mechanical energy?
a) Kinetic energy
b) Potential energy
c) Solar energy
d) None
Q19. The energy transformation in a microphone is:
a) Sound → Electrical
b) Electrical → Sound
c) Mechanical → Heat
d) Light → Electrical
Q20. Which of the following is true about work?
a) Work is scalar
b) Work is vector
c) Work has no unit
d) Work is always positive
Section B – True / False (10 Qs)
Q21. Work is said to be done only when displacement takes place in the direction of force. (T/F)
Q22. SI unit of power is Joule. (T/F)
Q23. Negative work is possible. (T/F)
Q24. Energy and work have the same units. (T/F)
Q25. Potential energy depends on mass and velocity. (T/F)
Q26. 1 Watt = 1 Joule/second. (T/F)
Q27. Work done in moving a body in a circular path is always zero. (T/F)
Q28. Kinetic energy depends only on velocity. (T/F)
Q29. 1 kWh is a smaller unit of energy compared to Joule. (T/F)
Q30. Mechanical energy is the sum of kinetic and potential energies. (T/F)
Section C – Fill in the Blanks (10 Qs)
Q31. Work done = ______ × displacement × cos θ.
Q32. The SI unit of energy is ______.
Q33. Potential energy = ______.
Q34. Kinetic energy = ______.
Q35. The rate of doing work is called ______.
Q36. SI unit of power is ______.
Q37. The commercial unit of electrical energy is ______.
Q38. 1 kWh = ______ J.
Q39. Energy can neither be created nor ______.
Q40. Work is positive when angle between force and displacement is ______.
Section D – Assertion Reason (10 Qs)
Q41. Assertion: Work done by a boy in lifting a load vertically upwards is positive.
Reason: Force applied and displacement are in the same direction.
Q42. Assertion: Kinetic energy depends on both mass and velocity of the body.
Reason: KE = ½ mv².
Q43. Assertion: Potential energy of a body on the ground is zero.
Reason: Height of the body above ground is zero.
Q44. Assertion: Power is the rate of doing work.
Reason: Its SI unit is watt.
Q45. Assertion: 1 kWh is a unit of power.
Reason: It is equal to 1000 Joule.
Q46. Assertion: Work is done when force is perpendicular to displacement.
Reason: cos 90° = 0.
Q47. Assertion: Mechanical energy is always conserved in absence of friction.
Reason: Mechanical energy = KE + PE.
Q48. Assertion: Work done is zero if displacement is zero.
Reason: W = F × d × cos θ.
Q49. Assertion: The faster a boy climbs the stairs, the more is his power.
Reason: Power = Work/Time.
Q50. Assertion: SI unit of power is Newton.
Reason: Power = Force × velocity.
Section E – Very Short Answer (1 mark, 10 Qs)
Q51. Define work.
Q52. What is SI unit of work?
Q53. Define 1 joule of work.
Q54. What is the condition for work to be done?
Q55. Define energy.
Q56. State the formula of kinetic energy.
Q57. Write the commercial unit of energy.
Q58. Define 1 kWh.
Q59. Define power.
Q60. State the work-energy theorem.
Section F – Short Answer (2 marks, 10 Qs)
Q61. Calculate the work done when a force of 20 N displaces a body 3 m in the direction of force.
Q62. Why is no work done when a body moves in a circular path under centripetal force?
Q63. Give two examples of negative work.
Q64. Distinguish between work and power.
Q65. A boy does 500 J of work in 50 seconds. Find his power.
Q66. What is meant by potential energy? Give its expression.
Q67. Write any two conditions for work to be done.
Q68. Calculate the work done by a force of 10 N when applied at an angle of 60° to displacement of 5 m.
Q69. A force of 50 N is applied on a body but the body does not move. How much work is done? Why?
Q70. A stone of mass 2 kg is raised through a height of 5 m. Calculate its potential energy.
Section G – Short Answer (3 marks, 10 Qs)
Q71. A force of 200 N displaces a body through 4 m in the direction of force. Calculate work done.
Q72. A body of mass 5 kg is moving with velocity 10 m/s. Calculate its kinetic energy.
Q73. A man of 60 kg climbs a staircase 5 m high in 5 seconds. Calculate the power developed.
Q74. Derive the expression for kinetic energy.
Q75. Differentiate between potential energy and kinetic energy.
Q76. A 500 W electric heater is used for 2 hours. Calculate the electrical energy consumed.
Q77. State and explain the law of conservation of energy with an example.
Q78. A pump is used to lift 500 litres of water to a height of 20 m in 10 seconds. Calculate the power of the pump.
Q79. A 60 W bulb is used for 10 hours. Calculate the energy consumed in kWh.
Q80. Explain why work done can be positive or negative with suitable examples.
Section H – Long Answer (4–5 marks, 10 Qs)
Q81. Derive the expression for potential energy.
Q82. Derive the relation KE = ½ mv².
Q83. Explain the work-energy theorem with an example.
Q84. A car of mass 1000 kg moving with a velocity of 72 km/h is stopped by brakes in 50 m. Calculate:
(i) Initial KE of the car
(ii) Work done by brakes
(iii) Force applied by brakes
Q85. What is meant by power? A motor does 1000 J work in 5 s. Find its power.
Q86. A hammer of mass 500 g falls freely from a height of 10 m. Find its KE when it just reaches the ground.
Q87. A body of mass 10 kg is dropped from a height of 20 m. Calculate the velocity with which it strikes the ground. Verify the law of conservation of energy.
Q88. Distinguish between commercial unit of energy and SI unit of energy. Why do we use kWh for electricity bills?
Q89. A 2 HP motor is used to lift 400 kg of water through 20 m in 40 s. Calculate efficiency of the motor if actual work done is 80% of the ideal.
Q90. State and prove the law of conservation of energy with the example of a simple pendulum.
Section I – Numerical Questions (10 Qs)
Q91. A force of 100 N displaces a body by 5 m in the direction of force. Find work done.
Q92. A 2 kg body moves with velocity of 5 m/s. Find its kinetic energy.
Q93. Find the work done in lifting a mass of 50 kg to a height of 10 m.
Q94. A pump is used to lift 1000 litres of water to a height of 20 m. Calculate the work done.
Q95. Calculate the power of a motor which lifts 100 kg water through 10 m in 20 s.
Q96. A body of mass 10 kg is moving with a velocity of 6 m/s. Find the work done in doubling its velocity.
Q97. An electric iron of 2 kW is used for 30 minutes. Calculate energy consumed in kWh.
Q98. A bullet of mass 10 g is moving with velocity of 500 m/s. Calculate its kinetic energy.
Q99. Calculate the potential energy of 2 kg body kept at a height of 15 m.
Q100. A 60 kg person climbs 20 steps each 0.25 m high in 20 seconds. Calculate power developed.