A horizontal plank has a rectangular block placed on it. The plank starts oscillating vertically and simple harmonically with an amplitude of 40 cm. The block just loses contact with the plank when the latter is at momentary rest Then.

Options

A. the period of oscillation is `2pi//5` s
B. the block wighs double its weight when the plank is at one of the positions of momentary at rest
C. the block weighs 1.5 times its weight on the plank half way down
D. the block weighs its true weight on the plank, when the later moves fastest

Answer

B

Explanation

At one of the extreme position, weight of block = restoring force. At the other extreme position, weight of block and restoring force both act downward direction. So, the force on block at is doubled than its weight.