Question

An apple gives $21kJ$ energy to a boy. How much height he can climb by using this energy. If his efficiency is $28\%$ ? (mass of boy $40kg$ )

• A. 22.5 m
• B. 15 m
• C. 10m
• D. 5m

Answer 1

Answer: (B)

Here : Energy of one apple $=2112J$
$=21\times 10^{3}J$
Efficiency of the boy $=28\%=0.28$
Mass of the boy $m=40kg$
Here the actual energy consumed by the boy is given by as
$=0.28\times 21000=5880J$ ...(1)
and the energy consumed by the boy in climbing $h$ meter height is given by
$=mgh=40\times 9.8\times hJ$ ...(2)
Equating equations (1) and (2) we get
$40\times 9.8\times h=5880J$
$h=\frac{5880}{40\times 9.8}=15m$