Question

A body falls from a height of $200m$. If gravitational attraction ceases after $2$ s, further time taken by it to reach the ground is $(g=10m{s}^{-2})$

• A. $5s$
• B. $9s$
• C. $13s$
• D. $17s$

Answer 1

The correct option is B $9s$

Given,

$u=0m/s$

$h=200m$

$t=2s$

$g=10m/s^2$

1st equation of motion,

$v=u+gt$

$v=0+10\times 2=20m/s$

Distance covered by ball in 2sec

3rd equation of motion,

$2gS=v^2-u^2$

$S=\frac{v^2}{2g}=\frac{20\times 20}{2\times 10}=20m$

The remaining distance from the ground,

$s=h-S=200-20$

$s=180m$

Time taken to reach the ground, $T=\frac{s}{v}$

$T=\frac{180}{20}=9sec$

The correct option is B.