In a children's park, there is a slide which has a total length of 10 m and a height of 8⋅0 m (figure 8-E3). A vertical ladder is provided to reach the top. A boy weighing 200 N climbs up the ladder to the top of the slide and slides down to the ground. The average friction offered by the slide is three tenth of his weight. Find (a) the work done by the ladder on the boy as he goes up; (b) the work done by the slide on the boy as he comes down. Neglect any work done by forces inside the body of the boy.
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Solution

Given,
$Length of the slide, l = 10 m Height of the slide, h = 8 m Weight of the boy, m g = 200 N$
Friction force,
$F = 200 \times (\frac{3}{10}) = 60 N$

(a) Work done by the ladder on the boy is zero, as work is done by the boy himself while going up.

(b) Work done against frictional force,
$W = μ R S = f l = (- 60) \times 10 = - 600 J$

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Given, Length of the slide, l=10 mHeight of the slide, h=8 mWeight of the boy, mg=200 N Friction force, F=200×310=60 N (a) Work done by the ladder on the boy is zero, as work is done by the boy himself while going up. (b) Work done against frictional force, W=μ RS=fl= -60×10 =-600 J