Kinematics

JEE Main level, single correct, medium

218 of 308

Question 218 of 308

Projectiles AA and BB are thrown at angles of 45∘45^{\circ} and 60∘60^{\circ} with vertical respectively from top of a 400m400m high tower. If their times of flight are same, the ratio of their speeds of projection vA:vB{v}_{A}:{v}_{B} is:

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Answer: (D) 1:21:\sqrt{2}

For same time of flight, vertical component of velocity of projection must be same. Therefore,
vAsin⁡45∘=vBsin⁡30∘⇒vAvB=1212⇒vAvB=12{v}_{A}\sin 45^{\circ}={v}_{B}\sin 30^{\circ} \Rightarrow \dfrac{{v}_{A}}{{v}_{B}}=\dfrac{\dfrac{1}{2}}{\dfrac{1}{\sqrt{2}}} \Rightarrow \dfrac{{v}_{A}}{{v}_{B}}=\dfrac{1}{\sqrt{2}}

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