AKU Entry Test Physics Work & Energy — Set 3

AKU Entry Test Physics Work & Energy — Set 3

1. Question 1

   Q1. A 5 kg block is lifted 2 m vertically. What is the work done against gravity?

   • A) 98 J
   • B) 100 J
   • C) 49 J
   • D) 20 J

   Answer: 98 J

   Explanation: Work done = mgh = 5 kg * 9.8 m/s^2 * 2 m = 98 J. Option B is incorrect due to rounding g to 10 m/s^2.

2. Question 2

   Q2. A force of 10 N acts on a body, displacing it 5 m at an angle of 60°. What is the work done?

   • A) 25 J
   • B) 43.3 J
   • C) 50 J
   • D) 21.65 J

   Answer: 25 J

   Explanation: Work done = F * d * cos(θ) = 10 N * 5 m * cos(60°) = 25 J. Option B is incorrect due to miscalculation.

3. Question 3

   Q3. A spring with k = 100 N/m is compressed by 0.2 m. What is the potential energy stored?

   • A) 2 J
   • B) 4 J
   • C) 1 J
   • D) 0.5 J

   Answer: 2 J

   Explanation: Elastic potential energy = 0.5 * k * x^2 = 0.5 * 100 N/m * (0.2 m)^2 = 2 J. Option B is incorrect due to calculation error.

4. Question 4

   Q4. A 2 kg object moves at 4 m/s. What is its kinetic energy?

   • A) 16 J
   • B) 8 J
   • C) 32 J
   • D) 4 J

   Answer: 16 J

   Explanation: Kinetic energy = 0.5 * m * v^2 = 0.5 * 2 kg * (4 m/s)^2 = 16 J. Option B is incorrect due to miscalculation.

5. Question 5

   Q5. A body of mass 10 kg is raised to a height of 2 m. If the acceleration due to gravity is 9.8 m/s^2, what is the work done?

   • A) 196 J
   • B) 200 J
   • C) 150 J
   • D) 100 J

   Answer: 196 J

   Explanation: Work done = mgh = 10 kg * 9.8 m/s^2 * 2 m = 196 J. Option B is incorrect due to rounding g to 10 m/s^2.

6. Question 6

   Q6. A car accelerates from 0 to 20 m/s in 4 s. If its mass is 1500 kg, what is the average power delivered?

   • A) 150 kW
   • B) 75 kW
   • C) 100 kW
   • D) 200 kW

   Answer: 75 kW

   Explanation: Average power = ΔKE / Δt = (0.5 * 1500 kg * (20 m/s)^2) / 4 s = 75 kW. Option A is incorrect due to miscalculation.

7. Question 7

   Q7. A 50 N force is applied at an angle of 30° to the horizontal, displacing a body 10 m horizontally. What is the work done?

   • A) 433 J
   • B) 500 J
   • C) 250 J
   • D) 375 J

   Answer: 433 J

   Explanation: Work done = F * d * cos(θ) = 50 N * 10 m * cos(30°) = 433 J. Option B is incorrect due to miscalculation.

8. Question 8

   Q8. A 1000 kg elevator is lifted 20 m in 10 s. What is the average power delivered?

   • A) 19.6 kW
   • B) 20 kW
   • C) 15 kW
   • D) 10 kW

   Answer: 19.6 kW

   Explanation: Average power = mgh / t = (1000 kg * 9.8 m/s^2 * 20 m) / 10 s = 19.6 kW. Option B is incorrect due to rounding g to 10 m/s^2.

9. Question 9

   Q9. A body is projected upwards with a velocity of 20 m/s. What is its kinetic energy at the highest point?

   • A) 0 J
   • B) 100 J
   • C) 200 J
   • D) 400 J

   Answer: 0 J

   Explanation: At the highest point, velocity = 0, so kinetic energy = 0. Option B is incorrect as it assumes some velocity at the highest point.

10. Question 10

    Q10. A force F = (2x + 3) N acts on a body, displacing it from x = 0 to x = 2 m. What is the work done?

    • A) 10 J
    • B) 8 J
    • C) 6 J
    • D) 4 J

    Answer: 10 J

    Explanation: Work done = ∫F dx = ∫(2x + 3) dx from 0 to 2 = [x^2 + 3x] from 0 to 2 = 10 J. Option B is incorrect due to miscalculation.

11. Question 11

    Q11. A 2 kg block is attached to a spring with k = 50 N/m. If it is displaced by 0.1 m, what is the elastic potential energy?

    • A) 0.25 J
    • B) 0.5 J
    • C) 0.1 J
    • D) 1 J

    Answer: 0.25 J

    Explanation: Elastic potential energy = 0.5 * k * x^2 = 0.5 * 50 N/m * (0.1 m)^2 = 0.25 J. Option B is incorrect due to miscalculation.

12. Question 12

    Q12. A body of mass 5 kg is moving with a velocity of 4 m/s. What is its kinetic energy?

    • A) 40 J
    • B) 20 J
    • C) 80 J
    • D) 10 J

    Answer: 40 J

    Explanation: Kinetic energy = 0.5 * m * v^2 = 0.5 * 5 kg * (4 m/s)^2 = 40 J. Option B is incorrect due to miscalculation.

13. Question 13

    Q13. A 100 g bullet is fired at 400 m/s. What is its kinetic energy?

    • A) 8000 J
    • B) 800 J
    • C) 4000 J
    • D) 16000 J

    Answer: 8000 J

    Explanation: Kinetic energy = 0.5 * m * v^2 = 0.5 * 0.1 kg * (400 m/s)^2 = 8000 J. Option B is incorrect due to miscalculation.

14. Question 14

    Q14. A 50 kg person climbs a staircase 4 m high in 10 s. What is the average power delivered?

    • A) 196 W
    • B) 200 W
    • C) 150 W
    • D) 100 W

    Answer: 196 W

    Explanation: Average power = mgh / t = (50 kg * 9.8 m/s^2 * 4 m) / 10 s = 196 W. Option B is incorrect due to rounding g to 10 m/s^2.

15. Question 15

    Q15. A spring is compressed by 0.2 m, storing 4 J of energy. What is its spring constant?

    • A) 200 N/m
    • B) 100 N/m
    • C) 50 N/m
    • D) 400 N/m

    Answer: 200 N/m

    Explanation: Elastic potential energy = 0.5 * k * x^2. Rearranging, k = 2 * energy / x^2 = 2 * 4 J / (0.2 m)^2 = 200 N/m. Option B is incorrect due to miscalculation.

16. Question 16

    Q16. A body is moving with a constant velocity. What is the net work done on it?

    • A) Positive
    • B) Negative
    • C) Zero
    • D) Depends on the force

    Answer: Zero

    Explanation: Since the body is moving with constant velocity, the net force acting on it is zero, so the net work done is zero. Option A is incorrect as it implies acceleration.

17. Question 17

    Q17. A 5 kg block is pulled 2 m along a frictionless surface by a 10 N force. What is the work done by the force?

    • A) 20 J
    • B) 10 J
    • C) 15 J
    • D) 25 J

    Answer: 20 J

    Explanation: Work done = F * d = 10 N * 2 m = 20 J. Option B is incorrect due to miscalculation.

18. Question 18

    Q18. A 2 kg object has a kinetic energy of 16 J. What is its velocity?

    • A) 4 m/s
    • B) 2 m/s
    • C) 8 m/s
    • D) 1 m/s

    Answer: 4 m/s

    Explanation: Kinetic energy = 0.5 * m * v^2. Rearranging, v = sqrt(2 * KE / m) = sqrt(2 * 16 J / 2 kg) = 4 m/s. Option B is incorrect due to miscalculation.

19. Question 19

    Q19. A body is projected upwards. At what point is its kinetic energy minimum?

    • A) At the ground
    • B) At the highest point
    • C) At the middle point
    • D) At the start

    Answer: At the highest point

    Explanation: At the highest point, velocity is zero, so kinetic energy is minimum. Option A is incorrect as it has maximum kinetic energy at the ground.

20. Question 20

    Q20. A 10 kg block is lifted 1 m in 2 s. What is the average power delivered?

    • A) 49 W
    • B) 50 W
    • C) 25 W
    • D) 100 W

    Answer: 49 W

    Explanation: Average power = mgh / t = (10 kg * 9.8 m/s^2 * 1 m) / 2 s = 49 W. Option B is incorrect due to rounding g to 10 m/s^2.