Question

A particle is projected at an angle of 45° 2m from the foot of a wall, just touches the top of the wall and falls on the ground on the opposite side at a distance 4 m from it. The height of wall is :

Moderate

Solution

Here, $θ = 45 °$ and $\frac{u^{2}}{g} = 6$ or u² = 6g, also $u \cos θ$ t = 2 or $t = \frac{2}{u \cos θ}$ and y = height of wall, then $y = u \sin θ . t + \frac{1}{2} {gt}^{2}$
$= usinθ \times \frac{2}{ucosθ} + \frac{1}{2} g \times \frac{4}{u^{2} \cos^{2} θ} or y = \frac{8}{3} m$
Hence (3) is the right choice.

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