Question

A ball projected from ground at an angle of ${45}^o$ just clears a wall in front. If point of projection is $4m$ from the foot of the wall and ball strikes the ground at a distance of $6m$ on the other side of the wall, the height of the wall is:

• A. $4.4m$
• B. $2.4m$
• C. $3.6m$
• D. $1.5m$

Answer 1

The correct option is B $2.4m$

$R=\frac{u^2\sin 2\theta }{g}=10m$

$u^2\sin 90=100$

$u^2=100$

$u=10m/s$

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

$=\frac{100\times {\sin }^2\left({45}^{\circ }\right)}{20}$

$=5\times \frac{1}{2}=2.5m$

Motion in the horizontal direction:

$ucos45\times t=4$

$⟹t=2\sqrt{2}/5$

Motion in the Vertical Direction :
$h=usin45-g{t}^2/2$
$⟹h=2.4m$