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 end of the plank
C. the right end of the plank
D. None of these

Answer

C

Explanation

In the ground frame
`: m_(A) Deltax_(A) + m_(B)Deltax_(B) + m_(P)Deltax_(P) = 0`
`rArr 40 xx 60 + 0 + 40 xx Deltax_(P) = 0`
`rArr Deltax_(P) = -60` (to the left)
Hence A & B meet at the right end.