Question

A body of mass $m$ when released from a height $h$, hits the ground with speed $\sqrt{gh}$. Find work done by resistive force.

• A. $\frac{mgh}{2}$
• B. $-\frac{mgh}{2}$
• C. $mgh$
• D. $-mgh$

Answer 1

Answer: (B)

$-\frac{mgh}{2}$

Identify initial and final state and identify all forces.
$W_g+W_{airres.}+W_{internalforce}=\Delta K$

$mgh+W_{airres.}+0=\frac{1}{2}m{\left(\sqrt{gh}\right)}^2-0$

$\Rightarrow w_{airres.}=-\frac{mgh}{2}$