Question

Two persons each of mass are standing at the two extremes of a railroad car of mass M resting on a smooth track. The person on the left jumps to the left with a velocity u. Thereafter second person jumps to right with same velocity u. Find the velocity of the train when both the persons have jumped off.

• A. towards left
• B. towards left
• C. towards right
• D. towards right

Answer 1

Answer: (B)

towards left

Answer 2

mu = −(M + m)v or v =

Negative sign means to words right

After the 2^nd person jumps, conserving momentum

(Now taking positive sign for right)

mu = Mv – Mv' or mu =

or v' = -

Negative sign shows towards left.