Question

Q5. A stone is dropped from a height of 80 m. Find
(i) Time of fall
(ii) Velocity after 2 seconds of free fall
(iii) Velocity with which it hits the ground.

Answer 1

Answer:

The height = h = 80 m.

The initial velocity = 0 m/s.

Now, We know that, t = √2h/g.

⇒ t = √2*80/9.8

⇒ t = √160/9.8

⇒ t = √16

⇒ t = 4 s

Now, We know that, v = u + gt.

⇒ v = 0 + 9.8*2

⇒ v = 19.6 m/s

Finding, the velocity with which it hits the ground.

⇒ v = u + gt

⇒ v = 0 + 9.8*4

⇒ v = 39.2 m/s

Hence, Time of fall = 4 s, velocity after 2 seconds of free fall = 19.6 m/s and velocity with which it hits the ground = 39.2 m/s.