PHYSICS SAMPLE QUESTIONS WORK, ENERGY AND POWER

Here are sample questions (with answers) for the Physics topic "Work, Energy and Power", styled for the exam formats of West African Examinations Council (WAEC), National Examinations Council (NECO) and Joint Admissions and Matriculation Board (JAMB).

These are practice questions only (not actual past papers). They follow the recent syllabus trends. According to the syllabi:
JAMB: Work, Energy & Power definitions; forms of energy; conservation; interpretation of area under force-distance curve; energy and society.

WAEC: Work done in a gravitational field; kinetic & potential energy; conservation of mechanical energy; concept of power.

🔹 SECTION A: Multiple Choice Questions

1. A force of 30 N acts on a body and moves it through a distance of 4 m in the direction of the force. What is the work done?
A. 120 J
B. 7.5 J
C. 30 J
D. 60 J
Answer: A. 120 J
Because Work = Force × Distance = 30 × 4 = 120 J.

2. The SI unit of power is:
A. Joule (J)
B. Watt (W)
C. Newton (N)
D. Joule-second (J·s)
Answer: B. Watt (W)
Because power = work done/time; unit = J/s = W.

3. Which of the following is a correct expression for kinetic energy?
A. mv²

B. ½mv²
C. mgh
D. F × d
Answer: B. ½mv² where m is the mass of the object and v is its velocity.

4. A machine lifts a load of 600 N through a vertical height of 5 m in 10 s. What is the power developed (assuming no losses)?
A. 300 W
B. 150 W
C. 600 W
D. 1000 W
Answer: A. 300 W
Work done = 600 N × 5 m = 3000 J. Power = 3000 J / 10 s = 300 W.

5. In the context of energy transformations: which statement is correct?
A. Energy can be created but not destroyed.
B. Energy can be destroyed but not created.
C. Energy can neither be created nor destroyed, only transformed.
D. Energy is always lost when used.
Answer: C. Energy can neither be created nor destroyed, only transformed.
(Principle of conservation of energy.)

6. The area under a force–distance graph represents:
A. Power
B. Energy
C. Force
D. Work
Answer: D. Work
Because Work = ∫F·dx; graph of F vs x → area = work.

7. A body of mass 2 kg moving at speed 10 m/s has a kinetic energy of:
A. 100 J
B. 200 J
C. 20 J
D. 50 J
Answer: A. 100 J

8. Which of the following is not a form of mechanical energy?
A. Potential energy
B. Kinetic energy
C. Thermal energy
D. Elastic energy
Answer: C. Thermal energy
Thermal energy is non-mechanical in many contexts (though related).

9. A machine lifts a load of 600 N through a height of 5 m in 10 s. Find the power developed.
Answer: 300 W

10. Which principle states that "Energy can neither be created nor destroyed, only transformed"?
Answer: Principle of conservation of energy

11. The area under a force–distance graph represents:
Answer: Work

12. If a body of mass 2 kg is moving at 10 m/s, what would be its kinetic energy?
Answer: 100 J

13. A 5 kg mass lifted 2 m. Calculate the work done.
Answer: 100 J

14. Power is defined as?
Answer: Rate of doing work

15. Define the following:

(i) Work done

(ii) Energy

(iii) Power

Answer:

Work done: The product of the component of force in the direction of displacement and the displacement.

Energy: The capacity of a body or system to do work.

Power: The rate at which work is done or energy is transferred (Work done per unit time)..

16. A 5 kg mass is lifted 2.5 m. Calculate (a) Work done (b) Power if lifted in 4 s.

17. A 1500 W motor lifts a load 12 m in 8 s. Determine the load.

18. Explain the principle of conservation of mechanical energy and give one practical example.

Answer:

The principle of conservation of mechanical energy states that in the absence of non-conservative forces (like friction), the total mechanical energy (sum of kinetic energy + potential energy) of a system remains constant.

Example: A pendulum swinging: At its highest point it has maximum potential energy and minimal kinetic; at lowest point it has maximum kinetic and minimal potential; total remains constant (neglecting air resistance & friction).

19 A 0.5 kg object thrown upward at 8 m/s. Find (a) initial KE (b) max height (c) PE at top.

20. A machine does 200 J of useful work when supplied 250 J. Find efficiency.

21. A 60 W bulb operates for 5 minutes. Calculate energy consumed in Joules.

22. A 50 kg person climbs stairs 5 m high in 10 s. Find power developed.

23. Distinguish between potential and kinetic energy with examples.

24. State and explain two non-mechanical forms of energy

25. A mass of 5 kg is lifted vertically through a height of 2.5 m. (Take g = 10.)
(a) Calculate the work done.
(b) If the lifting takes 4 s, calculate the power expended.
Solution:
(a) Work = m g h = 5 × 10 × 2.5 = 125 J
(b) Power = Work / time = 125 J / 4 s = 31.25 W

26. A 1500 W motor does work in lifting a load through 12 m in 8 s. Determine the load in newtons (ignore losses).
Solution:
Work done in 8 s = Power × time = 1500 × 8 = 12,000 J

Since work done = force × distance: Force = Work/distance = 12,000 J / 12 m = 1000 N
So the load = 1000 N.