Question

A stone is thrown from a bridge at an angle of ${30}^o$ down with the horizontal with a velocity of $25m/s$. If the stone strikes the water after $2.5$ seconds, then calculate the height of the bridge from the water surface.

Answer 1

$H=\frac{u^2{\sin }^2\theta }{2g}$

$H=\frac{{25}^2{\sin }^{2}30}{20}=7.97m$

From that height,

$u=0$

$s=\frac{1}{2}\times 10\times {2.5}^2=31.25m$

Height of bridge from river $=31.25-7.97=23.28m$