Question

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.
Figure

Answer 1

(a) The work done by the ladder on the boy is zero as he goes up

(b) The work done by the slide on the boy is -600 J as he comes down

Explanation:

Step 1:

Given data in the question  

L is Length of the slide

h is Height of the slide

mg is Weight of the boy

L = 10 m

h = 8 m

mg = 200 N

Step 2:

Friction force,

$F= 200\times \frac{3}{10}$

F = 20 × 3

F = 60 N  

(a) Work done on the ladder by the boy is zero, as the boy himself does the research while he's going up.  

(b) Work done against force of friction,

W = μ RS

W= Force × Length

W = (−60) × 10

W = − 600 J  

The work done by the slide on the boy is -600 J as he comes down.