Question

A ball is thrown vertically upwards with a velocity of 49m/s. calculate
a)the maximum height to which it rises
b)the total time it take to return to the surface of the earth


class 9, gravitation , page no-144

Answer 1

Explanation:

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