In this blog post, we explore Unit 4: Work, Energy, and Power from physics by discussing 50 multiple-choice questions (MCQs) along with their answers and explanations. These concepts are essential in understanding how forces cause displacement and the role of energy and power in physical systems.
1. The SI unit of work is?
A) Joule
B) Newton
C) Watt
D) Meter
Answer: A) Joule
Explanation: The SI unit of work is the Joule (J). It is defined as the wrk done when a force of 1 Newton moves an object by 1 meter in the direction of the force.
2. Work is done when?
A) An object is at rest.
B) There is no displacement.
C) A force causes displacement.
D) The object moves with constant velocity.
Answer: C) A force causes displacement.
Explanation: Wrk is done when a force is applied to an object and causes it to move in the direction of the force. If there is no displacement, no work is done.
3. If a person lifts a box from the ground to a height of 2 meters, the work done depends on?
A) The weight of the box.
B) The height the box is lifted.
C) The distance the box is moved horizontally.
D) Both A and B.
Answer: D) Both A and B.
Explanation: The work done in lifting the box depends on the weight (force) and the height the box is lifted, as work is given by W=F×dW = F \times dW=F×d, where FFF is the force and ddd is the displacement.
4. The energy possessed by an object due to its motion is called?
A) Kinetic energy
B) Potential energy
C) Thermal energy
D) Chemical energy
Answer: A) Kinetic energy
Explanation: Kinetic energy is the energy an object possesses due to its motion, defined as K.E=12mv2K.E = \frac{1}{2}mv^2K.E=21mv2, where mmm is the mass and vvv is the velocity.
5. What is the SI unit of power?
A) Joule
B) Watt
C) Newton
D) Meter
Answer: B) Watt
Explanation: The SI unit of power is Watt (W), which is defined as the rate at which work is done or energy is transferred. 1 W=1 J/s1 \, \text{W} = 1 \, \text{J/s}1W=1J/s.
6. The work-energy theorem states that?
A) Work done equals the change in kinetic energy.
B) Energy is conserved in all processes.
C) The net work done on an object is equal to the object’s final energy.
D) Work done equals the force applied.
Answer: A) Work done equals the change in kinetic energy.
Explanation: The work-energy theorem states that the net work done on an object is equal to the change in its kinetic energy. W=ΔK.EW = \Delta K.EW=ΔK.E.
7. A 10-kg object is lifted to a height of 5 meters. The work done in lifting the object is?
A) 50 Joules
B) 100 Joules
C) 500 Joules
D) 1000 Joules
Answer: B) 100 Joules
Explanation: The work done is calculated using the formula W=mghW = mghW=mgh, where mmm is the mass (10 kg), ggg is the acceleration due to gravity (9.8 m/s29.8 \, \text{m/s}^29.8m/s2), and hhh is the height (5 m).
W=10×9.8×5=100 JW = 10 \times 9.8 \times 5 = 100 \, \text{J}W=10×9.8×5=100J.
8. The potential energy of an object is given by?
A) 12mv2\frac{1}{2}mv^221mv2
B) mghmghmgh
C) mgvmgvmgv
D) mv2mv^2mv2
Answer: B) mghmghmgh
Explanation: Potential energy is the energy possessed by an object due to its position relative to other objects, especially in a gravitational field. It is given by PE=mghPE = mghPE=mgh, where mmm is mass, ggg is the gravitational acceleration, and hhh is the height.
9. The law of conservation of energy states that?
A) Energy can be created.
B) Energy can be destroyed.
C) Energy can neither be created nor destroyed, only converted.
D) Energy is independent of mass.
Answer: C) Energy can neither be created nor destroyed, only converted.
Explanation: The law of conservation of energy states that the total energy in a closed system remains constant; energy can be transformed from one form to another but cannot be created or destroyed.
10. A car is moving with a constant speed. The power exerted by the engine is?
A) Zero
B) Maximum
C) Constant
D) Increasing
Answer: C) Constant
Explanation: If the car is moving with a constant speed, the engine provides a constant amount of power to overcome resistive forces such as friction and air resistance.
11. The energy stored in a stretched or compressed spring is known as?
A) Kinetic energy
B) Gravitational potential energy
C) Elastic potential energy
D) Chemical energy
Answer: C) Elastic potential energy
Explanation: Elastic potential energy is the energy stored in an object when it is stretched or compressed, such as in a spring, and is given by E.P.E=12kx2E.P.E = \frac{1}{2}kx^2E.P.E=21kx2, where kkk is the spring constant and xxx is the displacement.
12. Which of the following has the highest kinetic energy?
A) A stationary car
B) A moving car with a small velocity
C) A moving car with a high velocity
D) A car at rest at the top of a hill
Answer: C) A moving car with a high velocity
Explanation: Kinetic energy depends on the velocity of the object. The car with the highest velocity will have the highest kinetic energy, as K.E=12mv2K.E = \frac{1}{2}mv^2K.E=21mv2.
13. Power is the rate at which?
A) Work is done.
B) Energy is transferred.
C) Force is applied.
D) Both A and B.
Answer: D) Both A and B.
Explanation: Power is the rate at which work is done or energy is transferred. It is defined as P=WtP = \frac{W}{t}P=tW, where WWW is work done and ttt is time.
14. An object moves with constant velocity. The work done by the net force acting on the object is?
A) Positive
B) Negative
C) Zero
D) Cannot be determined
Answer: C) Zero
Explanation: When an object moves with constant velocity, the net force acting on it is zero, and thus no work is done by the net force.
15. A machine does 500 J of work in 10 seconds. The power output of the machine is?
A) 50 W
B) 500 W
C) 5 W
D) 100 W
Answer: A) 50 W
Explanation: Power is given by P=WtP = \frac{W}{t}P=tW. Substituting W=500 JW = 500 \, \text{J}W=500J and t=10 st = 10 \, \text{s}t=10s, we get P=50010=50 WP = \frac{500}{10} = 50 \, \text{W}P=10500=50W.
16. A car engine is doing work at a constant rate. The energy consumed by the engine in 5 seconds is?
A) 0 J
B) 5 J
C) 10 J
D) Depends on the power output
Answer: D) Depends on the power output
Explanation: The energy consumed depends on the power output of the engine and the time for which it operates. The energy consumed is E=P×tE = P \times tE=P×t, where PPP is power and ttt is time.
17. The work done in lifting an object is stored as?
A) Kinetic energy
B) Thermal energy
C) Potential energy
D) Electrical energy
Answer: C) Potential energy
Explanation: When an object is lifted, the work done against gravity is stored as gravitational potential energy, PE=mghPE = mghPE=mgh.
18. A body of mass mmm is moving with velocity vvv. Its kinetic energy is?
A) 12mv\frac{1}{2}mv21mv
B) 12mv2\frac{1}{2}mv^221mv2
C) mv2mv^2mv2
D) 12m2v\frac{1}{2}m^2v21m2v
Answer: B) 12mv2\frac{1}{2}mv^221mv2
Explanation: The formula for kinetic energy is K.E=12mv2K.E = \frac{1}{2}mv^2K.E=21mv2, where mmm is the mass and vvv is the velocity of the object.
19. The rate of doing work is called?
A) Energy
B) Work
C) Power
D) Force
Answer: C) Power
Explanation: Power is the rate at which work is done or energy is transferred, expressed as P=WtP = \frac{W}{t}P=tW, where WWW is work and ttt is time.
20. The total mechanical energy of an object is the sum of?
A) Kinetic energy and potential energy
B) Kinetic energy and thermal energy
C) Potential energy and chemical energy
D) Kinetic energy and electrical energy
Answer: A) Kinetic energy and potential energy
Explanation: The total mechanical energy of an object is the sum of its kinetic energy and potential energy.
21. Which of the following is true about kinetic energy?
A) It depends on the mass of an object only.
B) It depends on the speed of an object only.
C) It depends on both mass and velocity.
D) It is constant for all objects.
Answer: C) It depends on both mass and velocity.
Explanation: Kinetic energy depends on both the mass of the object and the square of its velocity, as given by the formula K.E=12mv2K.E = \frac{1}{2}mv^2K.E=21mv2.
22. If the velocity of an object is doubled, its kinetic energy increases by a factor of?
A) 2
B) 4
C) 6
D) 8
Answer: B) 4
Explanation: Kinetic energy is proportional to the square of the velocity. Therefore, if velocity is doubled, the kinetic energy will increase by a factor of 22=42^2 = 422=4.
23. The power required to do 1000 J of work in 20 seconds is?
A) 5 W
B) 10 W
C) 50 W
D) 100 W
Answer: C) 50 W
Explanation: Power is calculated as P=WtP = \frac{W}{t}P=tW, where WWW is work and ttt is time. Substituting W=1000 JW = 1000 \, \text{J}W=1000J and t=20 st = 20 \, \text{s}t=20s, we get P=100020=50 WP = \frac{1000}{20} = 50 \, \text{W}P=201000=50W.
24. If a machine does 500 J of work in 5 seconds, the power output of the machine is?
A) 25 W
B) 50 W
C) 100 W
D) 200 W
Answer: B) 50 W
Explanation: Using the formula for power, P=WtP = \frac{W}{t}P=tW, where W=500 JW = 500 \, \text{J}W=500J and t=5 st = 5 \, \text{s}t=5s, we get P=5005=100 WP = \frac{500}{5} = 100 \, \text{W}P=5500=100W.
25. The kinetic energy of an object depends on?
A) Its mass and speed
B) Its mass and height
C) Its velocity and acceleration
D) Its displacement and velocity
Answer: A) Its mass and speed
Explanation: Kinetic energy depends on the mass of the object and the square of its velocity, as K.E=12mv2K.E = \frac{1}{2}mv^2K.E=21mv2.
26. The work done in lifting an object depends on?
A) The mass of the object
B) The height the object is lifted
C) The gravitational acceleration
D) All of the above
Answer: D) All of the above
Explanation: The work done in lifting an object is determined by the formula W=mghW = mghW=mgh, where mmm is mass, ggg is the acceleration due to gravity, and hhh is the height the object is lifted.
27. A spring with a spring constant of 100 N/m is compressed by 0.2 meters. The potential energy stored in the spring is?
A) 1 J
B) 2 J
C) 5 J
D) 10 J
Answer: A) 1 J
Explanation: Elastic potential energy is given by E.P.E=12kx2E.P.E = \frac{1}{2}kx^2E.P.E=21kx2, where kkk is the spring constant and xxx is the displacement. Substituting k=100 N/mk = 100 \, \text{N/m}k=100N/m and x=0.2 mx = 0.2 \, \text{m}x=0.2m, we get:
E.P.E=12×100×(0.2)2=1 JE.P.E = \frac{1}{2} \times 100 \times (0.2)^2 = 1 \, \text{J}E.P.E=21×100×(0.2)2=1J.
28. Which of the following statements is true about potential energy?
A) It is always positive.
B) It depends on the object’s speed.
C) It is stored energy due to an object’s position or state.
D) It is always zero.
Answer: C) It is stored energy due to an object’s position or state.
Explanation: Potential energy is the energy stored in an object due to its position (e.g., height in a gravitational field) or state (e.g., elastic potential energy in a spring).
29. Which of the following quantities is a vector?
A) Work
B) Power
C) Energy
D) Force
Answer: D) Force
Explanation: Force is a vector quantity because it has both magnitude and direction. Work, energy, and power are scalar quantities.
30. The work done by a constant force on an object is maximum when?
A) The force is applied at an angle of 0° to the displacement.
B) The force is applied at an angle of 45° to the displacement.
C) The force is applied at an angle of 90° to the displacement.
D) The object is at rest.
Answer: A) The force is applied at an angle of 0° to the displacement.
Explanation: The work done is maximum when the force is applied in the same direction as the displacement (0° angle), as W=F⋅d⋅cos(θ)W = F \cdot d \cdot \cos(\theta)W=F⋅d⋅cos(θ).
31. Which of the following is not a form of energy?
A) Kinetic energy
B) Gravitational potential energy
C) Electric field energy
D) Force
Answer: D) Force
Explanation: Force is not a form of energy. Energy is the ability to do work, whereas force is a vector that causes an object to move or accelerate.
32. A person applies a constant force of 20 N to push a box a distance of 3 meters. The work done by the person is?
A) 10 J
B) 30 J
C) 60 J
D) 80 J
Answer: C) 60 J
Explanation: Work is calculated as W=F⋅d⋅cos(θ)W = F \cdot d \cdot \cos(\theta)W=F⋅d⋅cos(θ), where F=20 NF = 20 \, \text{N}F=20N and d=3 md = 3 \, \text{m}d=3m, and the force is applied in the direction of displacement (θ=0∘\theta = 0^\circθ=0∘, so cos(0∘)=1\cos(0^\circ) = 1cos(0∘)=1).
Thus, W=20×3=60 JW = 20 \times 3 = 60 \, \text{J}W=20×3=60J.
33. The energy stored in an object due to its position in a field is called?
A) Kinetic energy
B) Potential energy
C) Thermal energy
D) Chemical energy
Answer: B) Potential energy
Explanation: Potential energy is the energy stored in an object due to its position in a force field (gravitational, elastic, etc.).
34. A ball is dropped from a height. As it falls, its potential energy is converted into?
A) Kinetic energy
B) Thermal energy
C) Sound energy
D) Chemical energy
Answer: A) Kinetic energy
Explanation: As the ball falls, its potential energy (due to height) is converted into kinetic energy (due to motion).
35. A 50 kg person climbs a staircase of height 10 meters. The work done in climbing the staircase is?
A) 500 J
B) 1000 J
C) 5000 J
D) 10000 J
Answer: C) 5000 J
Explanation: Work done is given by W=mghW = mghW=mgh, where m=50 kgm = 50 \, \text{kg}m=50kg, g=9.8 m/s2g = 9.8 \, \text{m/s}^2g=9.8m/s2, and h=10 mh = 10 \, \text{m}h=10m.
W=50×9.8×10=5000 JW = 50 \times 9.8 \times 10 = 5000 \, \text{J}W=50×9.8×10=5000J.
36. The energy that an object has due to its motion is known as?
A) Gravitational energy
B) Chemical energy
C) Kinetic energy
D) Elastic energy
Answer: C) Kinetic energy
Explanation: The energy possessed by an object due to its motion is called kinetic energy, expressed as K.E=12mv2K.E = \frac{1}{2}mv^2K.E=21mv2.
37. The potential energy of an object at the top of a hill is maximum when?
A) The object is at the bottom of the hill.
B) The object is halfway down the hill.
C) The object is at the top of the hill.
D) The object is in motion.
Answer: C) The object is at the top of the hill.
Explanation: Potential energy is highest when an object is at the highest point (top of the hill), as it depends on the height.
38. The power output of a machine is the rate at which?
A) Work is done
B) Energy is transferred
C) Both A and B
D) Force is applied
Answer: C) Both A and B
Explanation: Power is the rate at which work is done or energy is transferred, represented as P=WtP = \frac{W}{t}P=tW or P=EtP = \frac{E}{t}P=tE.
39. A force is applied to an object and it displaces the object. The work done by the force is zero if?
A) The force is applied in the direction of displacement.
B) The force is applied perpendicular to the displacement.
C) The object is at rest.
D) The object moves with constant velocity.
Answer: B) The force is applied perpendicular to the displacement.
Explanation: Work is zero if the force is perpendicular to the displacement, as W=F⋅d⋅cos(θ)W = F \cdot d \cdot \cos(\theta)W=F⋅d⋅cos(θ) and cos(90∘)=0\cos(90^\circ) = 0cos(90∘)=0.
40. A person does 200 J of work in 10 seconds. The power exerted by the person is?
A) 10 W
B) 20 W
C) 200 W
D) 100 W
Answer: B) 20 W
Explanation: Power is P=Wt=20010=20 WP = \frac{W}{t} = \frac{200}{10} = 20 \, \text{W}P=tW=10200=20W.
41. The energy required to move an object is equal to the work done. This is the principle of?
A) Conservation of energy
B) Work-energy theorem
C) Law of inertia
D) Newton’s third law
Answer: B) Work-energy theorem
Explanation: The work-energy theorem states that the work done on an object is equal to the change in its kinetic energy.
42. The force required to lift a 10 kg object vertically 5 meters against gravity is?
A) 10 N
B) 50 N
C) 100 N
D) 500 N
Answer: B) 50 N
Explanation: The force required is equal to the weight of the object, given by F=mgF = mgF=mg.
F=10×9.8=50 NF = 10 \times 9.8 = 50 \, \text{N}F=10×9.8=50N.
43. The mechanical advantage of a machine is defined as?
A) The ratio of output work to input work
B) The ratio of output force to input force
C) The ratio of input work to output work
D) The rate at which work is done
Answer: B) The ratio of output force to input force
Explanation: Mechanical advantage is the ratio of the force exerted by the machine (output force) to the force applied (input force).
44. The change in kinetic energy is equal to?
A) Work done
B) Potential energy
C) Total energy
D) Force multiplied by displacement
Answer: A) Work done
Explanation: According to the work-energy theorem, the change in kinetic energy of an object is equal to the work done on the object.
45. Which of the following is true about potential energy?
A) It depends only on mass
B) It depends only on velocity
C) It depends on both mass and height
D) It depends on temperature
Answer: C) It depends on both mass and height
Explanation: Gravitational potential energy depends on the mass of the object and the height from which it is lifted.
46. The unit of work and energy is the?
A) Watt
B) Joule
C) Newton
D) Meter
Answer: B) Joule
Explanation: The unit of both work and energy is the Joule (J). One joule is the work done when a force of one newton moves an object by one meter.
47. The work done in lifting an object is the same as the?
A) Potential energy
B) Kinetic energy
C) Total energy
D) Thermal energy
Answer: A) Potential energy
Explanation: The work done to lift an object against gravity is stored as gravitational potential energy.
48. The efficiency of a machine is given by the ratio of?
A) Input work to output work
B) Output work to input work
C) Output force to input force
D) Input force to output force
Answer: B) Output work to input work
Explanation: Efficiency is the ratio of useful output work to the total input work, often expressed as a percentage.
49. The energy needed to start an object moving is?
A) Potential energy
B) Kinetic energy
C) Work
D) Force
Answer: C) Work
Explanation: The energy needed to start an object moving is the work done to accelerate the object from rest.
50. The mechanical advantage of a lever is greater when?
A) The effort arm is shorter than the load arm
B) The effort arm is longer than the load arm
C) The load is heavier
D) The effort force is larger
Answer: B) The effort arm is longer than the load arm
Explanation: Mechanical advantage increases when the effort arm (distance from the fulcrum to the applied force) is longer than the load arm (distance from the fulcrum to the load).
Also Read: Unit 5: Motion of System of Particles and Rigid Body, Class 11 MCQs
You may also like to Read This: Class 11 political science MCQs all chapters