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. $(g=9.8{m/s}^2)$

Answer 1

Let height is $h$,

Vertical Velocity $=-25sin\left({30}^o\right)=-12.5m/s$

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

$\Rightarrow -h=-12.5\times 2.5-\frac{1}{2}\times 9.8\times {2.5}^2$

$\Rightarrow h=61.875m$