Question

a boy of mass 20 kg is standing on a free to move cart of mass 80kg. there is neglegible friction betveen the cart and the ground .initialy the boy is standing 25m away from the wall .if he moves 10m towards the wall the the final distance of his position from the wall is (correct answer-17)

Answer 1

Thus the final distance from the wall is 17 m.

Explanation:

Displacement of centre of mass of the cart + boy system parallel to the surface is zero.

Δxcm = m1Δx1 + m1Δx1 / m1 + m2

0 = m1Δx1 + m1Δx1 / m1 + m2

The distance moved by boy = 10 m

Distance moved by the cart = x  

Now displacement of man Δx1 = 10 − x

Displacement of cart w.r.t ground towards the wall is Δx2 = − x

m1Δx1 + m1Δx1 = 0

20 (10 − x) + 80 (−x) = 0

100 x = 200 x = 2 m

Displacement of man towards the wall is Δx1 = 10 − 2= 8 m

His distance from the wall X = 25 − 8 = 17 m

Thus the final distance from the wall is 17 m.