Question

A stone is projected from the ground with a velocity of $14m{s}^{-1}$ one second later it clean a wall $2m$ high. The angle of projection is $(g=10m{s}^{-2})$

• A. ${30}^{\circ }$
• B. ${45}^{\circ }$
• C. ${60}^{\circ }$
• D. ${15}^{\circ }$

Answer 1

The correct option is A ${30}^{\circ }$

Solution:

Given:

$u=14m{s}^{-1}$ , $g=10m{s}^{-2}$

It crosses the wall after time $t=1s$

It clears the wall of height 2m so $h=2m$

Equation for projection motion

$h=u_y\sin \theta t-\frac{1}{2}g{t}^2$ ……(i)

Putting the given values in the equation (i)

$2=14sin\theta \left(1\right)-\frac{1}{2}\times 10\times (1{)}^2$

$2=14sin\theta -5$

$7=14sin\theta$

$sin\theta =\frac{1}{2}$

$\theta ={30}^{\circ }$

Hence, the correct option is (a).