A man weight 60 kg climbs up a stair case with a 20 kg load on his head. The stair case has 20 steps and each step has a height 20 cm. The increase in potential energy of the man is (g=10ms−2)

A man weight 60 kg climbs up a stair case with a 20 kg load on his head. The stair case has 20 steps and each step has a height 20 cm. The increase in potential energy of the man is $(g = {10ms}^{- 2})$

A
3.5 k J
B
4.5 k J
C
8.1 k J
D
3.2 k J

Solution:

Mass m = mass of the man + mass of the load = 60 + 20 = 8 0kg

$h = 20 \times 20 = 400cm \Rightarrow 4m$

$g = 10 {ms}^{- 2}$

$P .E = mgh \Rightarrow 80×10×4$

$P .E = 3200 J$

$P .E = 3 .2kJ$

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