Question

A ball is gently dropped from a height of 20 m. If its velocity increases uniformly at the rate of $10m{s}^{-2}$, with what velocity will it strike the ground and time after which it will it strike the ground?

• A. 20 $m/s$, 2 s
• B. 24 $m/s$, $\sqrt{2}$ s
• C. 10 $m/s$, 4 s
• D. None of the above

Answer 1

The correct option is A 20 $m/s$, 2 s

Given, initial velocity of ball, $u=0$
Final velocity of ball, $v=?$
Distance through which the balls falls, $s=20m$
Acceleration $a=10m{s}^{-2}$
Time of fall, $t=?$
We know
$v^2-u^2=2as$
or $v^2-0=2\times 10\times 20=400$ or $v=20m{s}^{-1}$
Now using $v=u+at$ we have
$20=0+10\times t$ or $t=2s$