Question

A particle of mass $5\text{kg}$ is dropped from a tower of height $10\text{m}$. Find the difference of work done by gravity from point $A$ to $B$ $\left(W_{AB}\right)$ and change in potential energy from $A$ to $B$ $\left(U_{AB}\right)$.

• A. $10gh$
• B. $5gh$
• C. $-10gh$
• D. $-5gh$

Answer 1

The correct option is A $10gh$

Work done by gravity from $A$ to $B$:
$W_{AB}=mgh$
(+ve because displacement is in the direction of force)

Change in potential energy from $A$ to $B$
$U_{AB}=U_B-U_A$
$=mg(10-h)-mg\left(10\right)$
$=-mgh$

$\therefore W_{AB}-U_{AB}$
$=mgh-(-mgh)$
$=2mgh$
$=2\times 5\times gh$
$=10gh$