Imagine yourself standing in an elevator which is moving with an upward acceleration $a = 2 {m/s}^{2}$ . A coin is dropped from rest from the roof of the elevator, relative to you. The roof to floor height of the elevator is $1.5 m$ . (Take $g = 10 {m/s}^{2}$ ). Find the velocity of the coin relative to you when it strikes the base of the elevator.

6 m / s

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1.5 m / s

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2 m / s

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3 m / s

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Solution

The correct option is A $6 m/s$
Observing motion from lift reference frame.

Using Newton’s third equation of motion:
$v_{r}^{2} = u_{r}^{2} + 2 a_{r} s$
$u_{r} = 0$
$a_{r} = g - (- a) = (g + a)$
$v_{r}^{2} = 0 + 2 (g + a) h$
$v = \sqrt{2 (g + a) h} = \sqrt{2 \times 12 \times 1.5}$

$v = 6 m/s$

Final Answer: $(B)$

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Distance vs Displacement

Standard XII Physics

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The correct option is A 6 m/sObserving motion from lift reference frame. Using Newton’s third equation of motion: v2r=u2r+2ars ur=0 ar=g−(−a)=(g+a) v2r=0+2(g+a)h v=√2(g+a)h=√2×12×1.5 v=6 m/s Final Answer: (B)