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-- A lift whose floor to ceiling distance is d starts ascending with a constant acceleration of a. After a time t, a bolt falls from the ceiling of the lift, the time duration of free fall of the bolt will be (g is acceleration due to gravity)
A
√(2d/(g+a))
B
√(2d/(g-a))
C
√(d/(g+a))
D
√(d/(g-a))
Explanation
Using the concept of relative acceleration: a_rel = a_bolt - a_lift. Since bolt is in free fall (g downwards) and lift is accelerating upwards (a), a_rel = g - (-a) = g + a. Using s = 1/2 * a_rel * t^2 => d = 1/2 * (g+a) * t^2 => t = √(2d/(g+a)).
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