Energy Sources and Conservation

Question 1

A body falls freely from rest through a height H. At what height above the ground is its kinetic energy three times its remaining gravitational potential energy? Assume negligible air resistance.

• AH/4
• BH/3
• CH/2
• D3H/4

Question 2

A body is dropped from rest. At a point where it has lost 40% of its initial gravitational potential energy, what fraction of its initial potential energy remains as kinetic energy? Neglect air resistance.

• A20%
• B40%
• C60%
• D100%

Question 3

A machine receives 6000 J of energy. It transfers 1500 J to the surroundings as waste energy. What percentage of the input energy remains available as useful output?

• A25%
• B50%
• C75%
• D80%

Question 4

Which statement about a perpetual energy machine is consistent with the conservation of energy principle?

• AIt can produce unlimited useful work without energy input if friction is reduced
• BIt can create energy provided its output is mostly heat
• CIt cannot continuously deliver more energy than it receives
• DIt can produce energy indefinitely if its moving parts are light

Question 5

A moving object stops after sliding across a rough surface. Which statement is most accurate?

• AIts kinetic energy is destroyed by friction
• BIts kinetic energy is converted only into gravitational potential energy
• CIts mechanical energy is transferred partly into thermal energy and other forms
• DThe total energy of the object and surroundings becomes zero