An elevator is moving up with an acceleration a m/s2. A person inside the lift throws the ball upwards with a velocity um/s relative to himself. Then the time of flight of ball (in sec) will be:
A
ug+a
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B
ug−a
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C
2ug+a
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D
2ug−a
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Solution
The correct option is C2ug+a
The scenario for motion of ball is shown w.r.t lift frame.
with respect to lift frame:
initial velocity of ball =ur=um/s
acceleration of ball w.r.t lift: ar=−(g+a)m/s2 , −ve sign implies downward direction.
∴ applying the equation of motion in lift frame:
Sr=urt+12art2...(i) where Sr is the displacement in the lift frame.
For t=T=Time of flight, putting Sr=0 in equation (i), we get: