Two men `'A'` and `'B'` are standing on a plank. `'B'` is at the middle of the plank and `'A'` is at the left end of the plank. Lower surface of the plank is smooth. System is initially at rest and masses are as shown in Fig. `'A'` and `'B'` start moving such that the position of `'B'` remains fixed with respect to ground, then `'A'` meets `'B'`. Then the point where `A` meets `B` is located at

Options

A. the middle of the plank
B. `30 cm` from the left of the plank
C. the right end of the plank
D. none of these

Answer

C

Explanation

Taking the origin at the centre of the plank

`m_(1)/_\x_(1)+m_(2)/_\x_(2)+m_(3)/_\x_(3)=0 (:'x_(CM)=0)`
(Assuming the centre of the two men are exactly at the axis as shown in figure.
`60xx+40xx60+40(-x)=0impliesx=60cm`
Hence `A` and `B` meet at righht end of the plank