Question

A crane lifts weight of $75\,kg$ to a height of $15\,m$ in $15\,s$ . The power of the crane is (assuming $g=9.8\,m/s^{2}$ )

• A. $635\,\,W$
• B. $735\,\,W$
• C. $835\,\,W$
• D. $1135\,\,W$

Answer 1

Answer: (B)

$735\,\,W$

Answer 2

Work done by lift = change in PE of weight
$=mgh$ $=750\times 9.8\times 15=11025\,\,J$
So power of crane
$=\frac{\text{Energy used}}{\text{time}}$
$=\frac{11025}{15}=735\,W$