Question

A body falling from rest under gravity passes a certain point $P$.It was a distance of $400m$ from P and $4$ sec prior to passage through $P$ If $g=10m/se{c}^2$,then the height above the point $"P"$ from where the body began to fall is ?

• A. $900m$
• B. $320m$
• C. $680m$
• D. $720m$

Answer 1

The correct option is B $320m$

Distance travelled $=400m$.

Time$=4sec$

$B=10m/s^2$

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

$400=4u-1/2\times 10\times 16\times 5$

$400=4u-80$

$4u=480$

$u=120$

At highest point

$V=0$

$u^2=2\times g\times h$

$120\times 120=2\times 10\times h$

$h=720$

This height is from $400mtr$ below $P$

So height above $P$ is $720-400=320mtrs$