Question

A ball is dropped from the top of a building. The ball takes $0.5s$ to fall past the window of $3m$ in length at certain distance from the top of the building. ($g=10m/s^2$) How fast was the ball going as it passed the bottom of the window?

• A. 3.5 $m{s}^{-1}$
• B. 8.5 $m{s}^{-1}$
• C. 5 $m{s}^{-1}$
• D. 12 $m{s}^{-1}$

Answer 1

Answer: (B)

8.5 $m{s}^{-1}$

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

$3=u\left(0.5\right)+\frac{1}{2}\times 10(0.5{)}^2$

$3=\left(0.5\right)u+5\left(0.25\right)$

$\frac{1.75}{0.5}=u$

$\Rightarrow u=3.5m/s$
$v=u+gt$
$v=\left(3.5\right)+10\left(0.5\right)=8.5m/s$