Question

A perpetual-motion machine can never be built because it is not possible to eliminate...

A)Momentum
B)Inertia
C)Elasticity
D)Friction

Answer 1

The answer is: [C]: "elasticity" .
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Answer 2

D) Friction

Step-by-step explanation:

Perpetual Motion machine is that machine which will convert whole input energy into useful work.

So we will say that perpetual motion machine is an hypothetical machine which will be 100% efficient and it will convert whole input energy into useful work without any loss of energy.

we know that efficiency is given as

So in real conditions it is not possible to eliminate frictional force due to which we will not able to get 100% useful work so here in real conditions the efficiency is always less than 100%

so correct answer will be

D) Friction