Question

Choose the correct statement.

• A. work done by internal forces is equal to change in potential energy
• B. net work done on the body is equal to change in total mechanical energy
• C. net work done by all forces other than conservative forces is equal to change in total mechanical energy
• D. net work done on the system by internal forces is always zero

Answer 1

Answer: (C)

Let work done by all forces other than conservative forces $=W_{\text{others}}$
Work done by conservative forces, $W_{con}$ is negative of change in potential energy.
$W_{con}=-\Delta U$
From work energy theorem,
$W_{\text{by all forces}}=\Delta K$
$W_{\text{others}}+W_{\text{con}}=\Delta K$
$W_{\text{others}}-\Delta U=\Delta K$
$W_{\text{others}}=\Delta U+\Delta K$
Therefore work done by all forces other than conservative forces is equal to change in total mechanical energy.