Question

A stone is dropped from a height of 20 m. Calculate the velocity with which it hits the ground and the time taken. ($g=10m/s^2$)

• A. 15 m/s, 1.5 sec
• B. 20 m/s, 2 sec
• C. 35 m/s, 0.4 sec
• D. $10m/s^2$, 0.2 sec

Answer 1

The correct option is B 20 m/s, 2 sec

Distance (s) $=20m$
Initial velocity $=0m/s$
$g=10m/s^2$

By using the formula:
$v^2=u^2+2as$
$v^2=0^2+2\times 10\times 20$
$v^2=400$
$v^2=\sqrt{400}$
$v=20m/s$

For calculating time:
$V=u+at$
$20=0+10\times t$
$t=\frac{20}{10}$
$t=2sec$
The the stone will hit the ground with a velocity of $20m/s$ in sec.