A rope of negligible mass passes over a pulley of negligible mass attached to the ceiling, as shown in figure. One end of the rope is held by Student A of mass `70 kg`, who is at rest on the floor. The opposite end of the rope is held by Student `B` of mass `60 kg`, who is suspended at rest above the floor. The minimum acceleration `a_(0)` with which the Student `B` should climb up the rope to lift the Student A upward off the floor. `(g=10m//s^(2))`

Options

A. `(1)/(3)m//s^(2)`
B. `(2)/(3)m//s^(2)`
C. `(4)/(3)m//s^(2)`
D. `(5)/(3)m//s^(2)`

Answer

D

Explanation

For student `A` to just lift off the floor, tension `T` in string must be greater than or equal to `700 N`. The `F.B.D.` of student `B` is
Applying Newton's second law
`T-mg=ma rArr700-600=60a`
or `a=(5)/(3)m//s^(2)`