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Q.
How many $2.5\, kg$ bricks can man carry up a staircase $3.6\, m$ high in one hour if he works at an average rate of $9.8$ watt?
Work, Energy and Power
Solution:
Work done by man in one hour = power $\times$ time
$=9.8 \times 1 \times 60 \times 60 \, J$
Work done by man in raising one brick $=m g h$
$=2.5 \times 9.8 \times 3.6 \,J$
Number of bricks $N=\frac{9.8 \times 1 \times 60 \times 60}{2.5 \times 9.8 \times 3.6}=400$