Match the following :

Explanation

The block is at rest with respect to the box which is accelerated with respect to the ground. Hence, the acceleration of the block with respect to the ground is a downward. The forces on the block are

i. Mg downward (by the earth) and
ii. N upward (by the floor).
The equation of motion of the block is therefore
`Mg - N = Ma`
If N = Mg/4, the above equation gives `a=3g/4.` The block and hence the box should descend with an acceleration `3g/4`.