Question

A person standing on the edge of a cliff at some height above the ground throws the first ball straight up with an initial velocity u and then throws the second ball straight down with the same initial velocity u. Which of the following statements is TRUE regarding their velocities when they hit the ground?

• A. Both the balls will have the same velocity when they hit the ground.
• B. First ball will have higher velocity than the second.
• C. Second ball will have higher velocity than the first.
• D. Can’t say as final velocity depends on other factors as well.

Answer 1

The correct option is A

Both the balls will have the same velocity when they hit the ground.

For the first ball, consider when it is going upwards to reach the maximum height.

From third equation of motion, $v^2=u^2+2as$

0 = $u^2$ – 2 $\times$ 10 $\times$ s

u = $\sqrt{20}$ s

Now, consider second part where the ball from topmost point starts falling down and reaches the point from where it was thrown.

$v^2=u^2+2as$

$u_1^2$ = 0 + 20 s

$u_1$​ = $\sqrt{20}$ s

We see that, $u_1$ = u

Hence, their final velocities will be the same.