Question

a boy drops a ball from rest from the top of a building. at the same time, his friend throws a ball vertically upwards from the base of the building with speed 30m/s. The two balls collide after 1.8s. Find the distance from the ground to the top of the building.

Answer 1

Answer:

Given,

H=100m

For ball 1: u=0;g=10m/s

So, h

1

=u

1

+

2

1

gt

2

=0×t+

2

1

(10)

2

t

2

=5t

2

----------(1)

For ball2: u=40m/s;a=−10m/s

So, h

2

=u

2

+

2

1

at

2

=40×t+

2

1

(−10)

2

t

2

=40t−5t

2

---------(2)

h=h

1

+h

2

h=5t

2

+40t−5t

2

h=100m

100=40t

t=

2

5

=2.5s