Question

In the experiment of finding the reaction time of Sunil, his friend releases a scale from rest in between the fingers of Sunil and notices the scale to fall by a distance of 20 cm before being held by Sunil. The reaction time of Sunil is (Use g = 10 ms⁻²) *
(a) 0.1s
(b) 0.2s
(c) 0.3s
(d) 0.4s​

Answer 1

Given info : In the experiment of finding the reaction time of Sunil, his friend releases a scale from rest in between the fingers of Sunil and notices the scale to fall by a distance of 20 cm before being held by Sunil.

To find : the reaction time of Sunil is ...

solution : initial velocity of scale , u = 0 m/s

distance covered before being held by Sunil, s = 20 cm = 0.2 m

using formula, s = $ut+\frac{1}{2}at^2$

here, a = acceleration due to gravity = 10 m/s²

⇒ 0.2 = 0 + 1/2 × 10 × t²

⇒ 0.04 = t²

⇒ t = 0.2 sec

therefore the time of reaction of Sunil is 0.2 sec. hence option (b) is correct.