Question

A crane is used to lift $1000kg$ of coal from a mine $100m$ deep. If the time taken by the crane is 1 hr, then find the power of the crane, assuming the efficiency of the crane to be $80$%. ${g=9.8m/s}^2$

• A. $256.7watt$
• B. $240.3watt$
• C. $340.3watt$
• D. $376.1watt$

Answer 1

Answer: (C)

$340.3watt$

Work done $W=mgh=1000\times 100\times 9.8=9.8\times {10}^{5}J$

Since the efficiency is 80 % , So actual workdone is $W_a=\frac{9.8\times {10}^5}{0.8}$

So power $P=W_a/t=\frac{9.8\times {10}^5}{0.8\times 3600}=340.3watts$