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Question
A man is instructed to carry a package from the base camp at B to summit A of a hill at a height of 1200 metres. The man weighs 800 N and the package weighs 200 N. If g = 10 m/s2,
- how much work does man do against gravity?
- what is the potential energy of the package at A if its is assumed to be zero at B?
Solution
Weight of the man (W1) = 800 N
Weight of the package (W2) = 200 N
Height of hill (h) = 1200 m
Acceleration due to gravity (g) = 10 m/s2
(1) So total weight,
W = W1 + W2
W = (800 + 200) N
W = 1000 N
Since we know that, weight w = m × g
Thus, wt = m × g = 1000 N
Height climbed from the base camp at B to summit A, h = 1200 m
Work done in lifting a body = Weight of body × Vertical distance
= 1000 × 1200 J
= 1200000
= 12 × 105 J
(2) We can calculate potential energy as
P. E = m × g × h
P. E = (200) (1200) J
= 240000 J
= 2.4 × 105 J
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