Question

Identify the correct reason of the following statement: 'All machines require a constant input of energy to keep running.'

• A. Energy is being destroyed in the machine.
• B. Energy is always being lost through friction.
• C. Not enough energy is created by the machine to keep it running.
• D. It is a perpetual motion machine.
• E. The first law of thermodynamics does not apply to machines.

Answer 1

Answer: (B)

Energy is always being lost through friction.

First Law of Thermodynamics does apply to machines. However here in machines, friction is always present between machine parts, that causes heat to be dissipated due to this. Thus work is being done against friction, and in accordance with the First Law of Thermodynamics, constant input of energy is required to keep the machine output the same.