Chapter 9

NCERT
Class 9
Science
Solutions
13. A ball is thrown vertically upwards with a velocity of 49 m/s Calculate. (i) The maximum height to which it rises. (ii) The total time it takes to return to the surface of the earth.

Question:

A ball is thrown vertically upwards with a velocity of 49 m/s Calculate.

(i) The maximum height to which it rises.

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

Answer:

According to question, u = 49 m/s

at the maximum height

v = 0, g = 9.8 m/s2

(i) From the equation

v2 = u2 – 2gh

0 = (49)2 - 2 x 9.8 x h

19.6h = 49 x 49

h = (49 x 49) / 19.6

h = 122.5 m

(ii) While throwing upward

v = u - gt

t = (u-v)/(-g)

t = -49/-9.8

t = 5s

∵ The ball takes the same time to reach the surface from the maximum height

∴ total time = (5 + 5)s = 10s

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