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 the work done by gravity on the block is

Options

A. The vector will become parallel to each other at t = 4s
B. The vectors will never become perpendicular to each other
C. The vectors will become perpendicular to each other at t = 1/4 s
D. The vector will become parallel to each other at t = 2 s

Answer

c

Explanation

For parallel
`t^(3)=-16` (not possible ast `ge` 0)
for perpendicular `bar a. barb =0 = 8t^(3)-2t^(2), t=1//4`