Question

A stone is thrown from a bridge at an angle of ${30}^o$ with the horizontal in the downward direction with a speed of $25m/s$. If the stone strikes the water after $2.5sec$, then calculate the height of the bridge from the water surface $(g=9.8{m/s}^2)$

• A. $61.9m$
• B. $35m$
• C. $70m$
• D. $None$

Answer 1

The correct option is A $61.9m$

Vertical component of initial velocity is $u\times sin\theta =$ $25\times \frac{1}{2}$

Time taken is 2.5 seconds

Height is $u\times t+\frac{1}{2}\times a\times t\times t$

H=$25\times \frac{1}{2}\times 2.5+\frac{1}{2}\times 9.8\times 2.5\times 2.5=61.875$ m