Question

A stone projected at an angle $\theta$ with horizontal from the roof of a tall building falls on the ground after three seconds. Two seconds after the projection it was again at the level of projection. Then the height of the building is:

• A. $15m$
• B. $5m$
• C. $25m$
• D. $20m$

Answer 1

The correct option is A $15m$

Let the Time taken for projectile motion be 'T' and time taken for descend be 't'.

$\begin{array}{c}T=\frac{2u\sin \theta }{g}=2\\ u\sin \theta =10\\ wkt,\\ s=ut+\frac{1}{2}a{t}^2\\ H=-u\sin \theta \times 3+\frac{1}{2}\times 10\times 1^2\\ H=15m\end{array}$