Question

A ball $A$ is thrown vertically upward with speed $u$ . At the same instant, another ball $B$ is released from rest at height $h$ . At time $t$ , the speed of $A$ relative to $B$ is (Assume both are in the air)

• A. $u$
• B. $u-2gt$
• C. $\sqrt{u^{2} - 2 g h}$
• D. $u-gt$

Answer 1

Answer: (B)

From equation of motion, we have
$v = u + gt$
where $u$ is initial velocity and $t$ is time.
For ball $A , v _{ A }= u - gt$
For ball $B , v _{ B }=0+ gt$
$\therefore$ Relative speed