Question

a ball is thrown vertically upwards with velocity 15 m/s from top of the building , reaches the foot of building in 5 sec . find height of the building and the velocity with which the ball hits the ground (g = 10 m/s )​

Answer 1

Given parameters:

Initial velocity of the ball (u) = 49m/s.

The velocity of the ball at maximum height (v) = 0.

g = 9.8m/s2

Find out:

1) The maximum height to which it rises.

2) The total time it takes to return to the surface of the earth.

Solution:

Let us consider the time is t to reach the maximum height H.

Consider a formula,

2gH = v2 – u2

2 × (- 9.8) × H = 0 – (49)2

– 19.6 H = – 2401

H = 122.5 m

Now consider a formula,

v = u + g × t

0 = 49 + (- 9.8) × t

– 49 = – 9.8t

t = 5 sec

Answer:

(1) The maximum height to which the ball rises = 122.5 m

(2) The total time ball takes to return to the surface of the earth = 5 + 5 = 10 sec.