Free Work and Energy MCQs with Answers

• A. always greater than 100 per cent
• B. the ratio of useful output energy to total input energy, expressed as a percentage
• C. the ratio of input to output
• D. equal to the power output

Explanation: Efficiency can never exceed 100 per cent, because energy is conserved and some is always lost to friction, sound and heat.

• A. 80 per cent
• B. 125 per cent
• C. 100 per cent
• D. 20 per cent

Explanation: Dividing 400 by 500 and multiplying by 100 gives 80 per cent, with the remaining 100 J lost mainly as heat.

• A. energy is destroyed
• B. energy is transferred to the surroundings as heat and sound by air resistance and friction at the pivot
• C. gravity weakens
• D. the mass of the bob decreases

Explanation: Energy is conserved overall, but the mechanical energy of the pendulum is gradually converted into thermal energy of the air and the…

• A. acts in the same direction as the displacement
• B. has a component opposite to the displacement, so it removes energy from the body
• C. does no work at all
• D. acts at right angles to the displacement

Explanation: Friction and air resistance always oppose the motion and therefore always do negative work, reducing the kinetic energy.

• A. kx
• B. half kx squared
• C. kx squared
• D. half kx

Explanation: The force rises linearly from zero to kx, so the average force is half of kx and the work done is half k x squared, which is also the area…

• A. 5 m per second
• B. 10 m per second
• C. 50 m per second
• D. 100 m per second

Explanation: From half mv squared equal to 50, v squared is 100 and v is 10 m per second.

• A. Solar
• B. Wind
• C. Coal
• D. Hydroelectric

Explanation: Coal is a fossil fuel formed over hundreds of millions of years, so it is consumed far faster than it can be replaced and its combustion…

• A. the length of the slope
• B. the vertical height dropped, but not on the angle of the slope
• C. the mass of the body
• D. the angle only

Explanation: Energy conservation gives half mv squared equal to mgh, so the mass cancels and only the height matters, which means a gentle ramp and a…

• A. can be created when needed
• B. can be destroyed by friction
• C. can be transformed from one form to another but the total remains constant
• D. always increases in an isolated system

Explanation: Friction does not destroy energy; it converts organised kinetic energy into disordered thermal energy, which is harder to use but is still…

• A. P/2m
• B. P2/2m
• C. 1/2 Pm2
• D. 1/2 P2m

Explanation: Kinetic energy is half mv squared and momentum is mv, so substituting v equal to P over m gives half m multiplied by P squared over m…

• 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…

• 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…

• 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.

• A. 50%
• B. 100%
• C. 23.6%
• D. 29.4%

Explanation: Carnot efficiency is η = 1 - Tc/Th, with temperatures in kelvin. Here Th = 150°C + 273 K = 423 K and Tc = 50°C + 273 K = 323 K, so η = 1 -…

• A. efficiency
• B. coefficient of performance
• C. both A and B
• D. not described

Explanation: A refrigerator is assessed by its coefficient of performance, COP = heat removed from the cold space ÷ work input, rather than by…

• A. Fusion
• B. Polymerization
• C. Crystallization
• D. Subtraction

Explanation: Polymerization joins many small molecules called monomers to form a large molecule called a polymer.

• A. direct combustion
• B. fermentation
• C. both A and B
• D. none of these

Explanation: Biomass can produce fuel by direct combustion, such as burning wood or crop waste, and by fermentation, which produces fuels such as…

• A. Twice
• B. Thrice
• C. Four times
• D. Sixteen times

Explanation: For a fixed mass, kinetic energy is K = p²/(2m), so it depends on the square of momentum.

• A. K.E hoop = K.E disc
• B. K.E hoop = 2K.E disc
• C. K.E hoop = 1/2K.E disc
• D. K.E hoop = 4K.E disc

Explanation: Rotational kinetic energy is 1/2 Iω². For the same mass and radius, a hoop has I = MR² while a disc has I = 1/2 MR², so K.E hoop = 2K.E…

• A. its K.E is doubled
• B. its acceleration is doubled
• C. its P.E is doubled
• D. its momentum is doubled

Explanation: Momentum is p = mv, so doubling the speed while keeping mass constant doubles the momentum.