Question

How long does it take for the ball to strike the ground?

• A. $4.52s$
• B. $5s$
  
• C. $6s$
  
• D. $7s$
  

Answer 1

The correct option is A $4.52s$

Given,

Initial velocity, $u=0$ (at rest)

Height, $h=100m$

Acceleration due to gravity, $a=g=9.8m/s^2$

Time, $t$

Using Newton' second equation of motion,

$s=ut+\frac{1}{2}a{t}^2$

$h=\frac{1}{2}a{t}^2$

$⟹t=\sqrt{\frac{2h}{a}}$

$t=\sqrt{\frac{2\times 100}{9.8}}$

$t=\sqrt{20.408}$

$t=4.52s$