Question

A ball is projected at an angle ${45}^{\circ }$ with horizontal from a point on ground $10m$ away from a vertical wall. It just crosses the wall to land on the ground at a distance $40m$ from the wall on other side. Then the height of the wall is:

• A. $20m$
• B. $4m$
• C. $8m$
• D. $10m$

Answer 1

The correct option is C $8m$

Equation of projectile is

$y=n\tan \theta \left(1-\frac{n}{R}\right)$

Total distance the ball covers before falling $=10+40=50$ m

$\therefore$Range $=50$m

Now, $y=10\tan {45}^0\left(1-\frac{10}{50}\right)$

$=10\times 1\times \frac{40}{50}=2\times 4=8m$

Height of wall $=8$ m

Hence Option $C$ is correct.