Question

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

Answer 1

Answer:

V2 = 1 m/s

Explanation:

mass of the child ( m1 ) = 4 kg

initial velocity ( u1 ) = 10 m/s

final velocity ( v1 ). = 0 m/s

Then,

mass of the plank ( m2 ) = 40 kg

initial velocity ( u2 ) = 0 m/s

final velocity ( v2 ) = ?

Now,

According to law of conservation of momentum :

m1u1 + m2u2 = m1v1 + m2v2

put the value,

4(10) + 40(0) = 4(0) + 40(v2)

40 + 0 = 0 + 40v2

40 = 40v2

v2 = 40/ 40

v2 = 1 m/s

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