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Question

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

A
4.4 m
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B
2.4 m
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C
3.6 m
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D
1.6 m
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Solution

## The correct option is B 2.4 m Here, Range=4 m+6 m=10 m As the ball is projected at an angle 45∘ to the horizontal, Therefore, Range=4H 10=4H⇒H=104=2.5 m Maximum height, H=u2sin2θ2g ∴u2=H×2gsin2θ=2.5×2×10(1√2)2=100 u=√100=10 ms−1 From trajectory formula, y=xtanθ−gx22u2cos2θ So, the height of the wall PA is, h=(OA) tanθ−g(OA)22u2cos2θ h=(4×1)−12×10×42102×(1/√2)2 ∴h=2.4 m Hence, option (B) is correct.

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