Free Work and Energy MCQs with Answers

31. Earth receives large amount of energy directly from:

• A. Wind
• B. Water
• C. Sun
• D. Moon

Explanation: Solar radiation is the primary energy input to the Earth, and wind and flowing water are themselves driven by the uneven solar heating of the atmosphere and oceans, which makes them secondary rather than direct sources. The Sun's energy comes from the fusion of hydrogen into helium in its core. Tidal energy is the one significant contribution that traces back to the Moon instead.

32. The work done by the gravitational force on an object as it moves from a reference level to a higher point is:

• A. Always positive
• B. Always negative
• C. Zero
• D. Depends on the path taken

Explanation: Gravity acts downwards while the displacement is upwards, so the force has a component opposite to the motion and the work it does is negative, which is exactly why the potential energy of the object increases. Coming back down, gravity does positive work. Because gravity is a conservative force, the work depends only on the change in height and not on the path.

33. A 0.5 kg ball moving at 6 m/s has kinetic energy

• A. 9 J
• B. 18 J
• C. 6 J
• D. 3 J

Explanation: Kinetic energy is half mv squared, so half multiplied by 0.5 multiplied by 36 gives 9 J. Forgetting the factor of one half gives 18 J, which is the commonest slip. Note that the momentum of the same ball would be 3 kg m per second, which is why 3 also appears as a distractor.