Hard

Question

A projectile is fired at an angle θ with the horizontal. Find the condition under which it lands perpendicular on an inclined plane inclination α as shown in figure.       

Options

A.sin α = cos (θ − α)
B.cos α = sin (θ − α)
C.tan α = cot (θ − α)
D.cot (θ − α) = 2tan α

Solution

Applying equation of motion perpendicular to the incline for y = 0.
0 = V sin (θ − α)t + (− g cos α) t2   

⇒    t = 0     &
At the moment of striking the plane, as velocity is perpendicular to the inclined plane hence component of velocity along incline must be zero.
0 = v cos (θ − α) + ( − g sin α).
v cos (θ − α) = tan α. 2V sin (θ − α)
cot (θ − α) = 2 tan α    Ans. (D)

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