A block of mass M is kept in elevator (lift) which starts moving upward with constant acceleration b as shown in figure. Initially elevator at rest. The block is observed by two observers A and B for a time interval `t=0` to `t=T`. Observer B is at rest with respect to elevator and observer A is standing on the ground.
Q. The observer A finds that work done by normal reaction acting on the blocks is

Options

A. `(1)/(2)M(g+b)^(2)T^(2)`
B. `-(1)/(2)M(g+b)^(2)T^(2)`
C. `(1)/(2)M(g+b)bT^(2)`
D. `(1)/(2)M(g+b)bT^(2)`

Answer

C

Explanation

The normal reaction acting on the block is `M(g+b)` in upward direction. The upward displacement of the block is `(1)/(2)bT^(2)` hence the work done by normal reaction is `M(g+b)xx(1)/(2)bT^(2)`