Q7 of 35 Page 55

A ball which is thrown vertically upwards reaches the roof of a house 100m high. At the moment this ball is thrown vertically upward, another ball is dropped from rest vertically downward from the roof of the house. At which height the ball will pass each other?

The following equations will be used:




Where u = Initial Velocity; v = Final Velocity; a = Acceleration; t = time; s = Distance;


There are two balls


Let us name them as A and B


A is thrown up and reaches maximum height of 100 m


At max height = h


v = 0


u = ?


s = h = 100 m


a = –g


Using equations of motion:





..1


B is dropped from a height 100 m



Ball A:



Here, s = 100–x; a = g; u = 0


So,


..2


Ball B:



Here, s = x; a = –g; u = 44.27 ms–1;


So,


..3


From 2 and 3, we get:




So,



So ball reaches the height of 74.97 m


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