An elevator car, whose floor to ceiling distance is equal to 2.7 m, starts ascending with constant acceleration of 1.2 ms–2. 2 sec after the start, a bolt begins falling from the ceiling of the car. The free fall time of the bolt is

(1) $\sqrt{0.54}\text{\hspace{0.17em}}s$

(2) $\sqrt{6}\text{\hspace{0.17em}}s$

(3) 0.7 s

(4) 1 s

Concept Videos :-

#45-Relative motion
#46-Relative motion-1
#47-Relative motion-2
#48-Relative motion-3
#49-Relative motion-4
#50-Relative motion-5

Concept Questions :-

Relative motion in 1-D

(3)

Using relative motion concept,

$t=\sqrt{\frac{2h}{\left(g+a\right)}}=\sqrt{\frac{2×2.7}{\left(9.8+1.2\right)}}=\sqrt{\frac{5.4}{11}}=\sqrt{0.49}=0.7\mathrm{sec}$

As u = 0 and lift is moving upward with acceleration

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