Ncert Exercises & Solutions

Q.29 Calculate the power of a crane in watts, which lifts a mass of 100 kg to a
height of 10 m in the 20s.

Hint: Work done by crane = change in potential energy of the mass.

Step 1: Find the power of the crane

Given,

$\begin{array}{l} mass = m = 100 kg \\ height = h = 10 m time duration t = 20 s \\ power = Rate of work done \\ = \frac{change of PE}{time} = \frac{mgh}{t} \\ = \frac{100 \times 9 .8 \times 10}{20} \\ = 5 \times 98 = 490 W \end{array}$

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