Question

In the figure given below a child of mass 4kg is standing on a wooden plank of mass 40kg which is kept at rest on a horizontal smooth ground. If child walks on the plank with a velocity of 10m/s with respect to plank then the velocity of the plank w.r.t.ground will be​

Answer 1

Given:

Mass of the child = 4 kg

Mass of the wooden plank = 40 kg

Velocity of child with respect to plank = 10 m/s

To find:

Velocity of plank w.r.t ground.

Solution:

V child w.r.t plank = V child w.r.t ground + V plank w.r.t ground

10 = v + u

where v = V child w.r.t ground

V= V plank w.r.t ground

Initially the system is at rest, by conservation of momentum we get:

0 = mv - Mu

Mu = mv

m(10 - u )= Mu

10m - mu = Mu

40 + 4u = 40u

u = 40/44

u = 10/11 m/s

Therefore, the velocity of plank w.r.t ground is 10/11 m/s.

Answer 2

Explanation:

answer is in the attachment