Question

A body, when dropped from a certain height, falls to the ground in 4 s. What is the time taken by the body to cover the last 100 cm? $(Takeg={10ms}^{-2})$

• A. $0.65s$
• B. $0.15s$
• C. $0.125s$
• D. $0.025s$

Answer 1

The correct option is D $0.025s$

Let Height $h$ from a body is dropped.

Using $s=ut+\frac{1}{2}a{t}^2$ $\Rightarrow -h=0\times 4-\frac{1}{2}g\times 4^2$ $\Rightarrow h=80m$,

Let time $t$ to cover the 79$m$.

Using $s=ut+\frac{1}{2}a{t}^2$ $\Rightarrow -79=0\times t-\frac{1}{2}g\times t^2$ $\Rightarrow t=\sqrt{\frac{79}{5}}$= 3.975 $s$

$\therefore$ Required time= $4-3.975=0.025$ $s$