Question

A crane lifting a box of mass $100kg$ at a constant velocity to a height of $8m$ over a time of $4s$. The crane then holds the box for $20s$.
Calculate the power required by the crane in lifting the box?

• A. $0W$
• B. $2.0\times {10}^{3}W$
• C. $3.2\times {10}^{3}W$
• D. $2.0\times {10}^{4}W$
• E. $3.2\times {10}^{4}W$

Answer 1

Answer: (B)

$2.0\times {10}^{3}W$

Given : $m=100kg$ $h=8m$ $t=4$ s

Workdone by crane in lifting the box $W=mgh=100\times 10\times 8=8000$ J

$\therefore$ Power required by the crane $P=\frac{W}{t}=\frac{8000}{4}=2\times {10}^3$ $W$