Question

a person in lift which ascents up with acceleration 10 m/s2 drops a stone from a height 10 m.the time of descent is_________ [ g= 10m/s2] A. 1s B. 2s C. 15m D. 20m

Answer 1

Acceleration of the stone = 10 m/s².

Height = 10 m.

Initial velocity = 0

Using the Newton's second equation of the motion,

S = ut + 1/2 at²

⇒ 10 = 0 + 1/2 × 10 × t²

⇒ t² = 2

∴ t = √2 seconds.

≈ 1.414 seconds.

Hence, the time of Descent is √2 seconds or 1.414 seconds.

Since, there is no exact option. Thus we need to round off the time. ∴ Time of Descent = 1 seconds.

Hence, Option (A). is correct.

Hope it helps.

Answer 2

Answer:

1s

Explanation:

The overall acceleration of the motion is(pseudo acceleration)i.e

g+a=10+10=20m/s

Now,

time of decent= sqrt(2h/g+a)

=sqrt(

$2 \times 10 \div 20$

=1s

HOPE THIS HELPS.....:)