A ball was thrown from height H and the ball hits the floor with velocity 10(^i−^j) m/s,1.5 sec after its projection. Find initial speed of ball.
A
10√5 m/s
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B
5√5 m/s
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C
15 m/s
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D
30 m/s
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Solution
The correct option is B5√5 m/s Given that, 1.5 sec after projection, →vx=10^i →vy=−10^j→a=−g^j=−10^j Now, (→uy)=→vy−→at=−10^j−(−10^j)×(1.5) ⇒→uy=5^j As there is no acceleration in horizontal direction, −→ux=→vx=10^i Initial velocity vector, →u=−→ux+→uy=10^i+5^j⇒|→u|=5√5 m/s