A cord is used to lower vertically a block of mass M through a distance d at a constant downward acceleration `(g)/(4)` Consider the following statements:
1. The block is freely falling under gravity.
2. The cord is doing work one the block.
3. The amount of work done is `((3Mgd))/(4)`

Options

A. 1 and 2 only
B. 1 and 3 only
C. 2 and 3 only
D. 1, 2 and 3

Answer

C

Explanation

As the mass Mis accelerating downwards Hence, the net force,
`F=Mg-Ma=Mg-(Mg)/(4)=(3)/(4)Mg`
Thus the work done by the cord on the block in moving the distance d.
`W=F.S=(3)/(4)Mgd.`