A rubber ball is shot straight up from the ground with a speed of 12 m/s. Simultaneously, a second identical rubber ball is dropped from rest exactly 7 m directly above the first ball. At what height (in m) do the two balls collide?

6.17 m

Explanation:

We are given that

Initial speed of rubber ball, u=12 m/s

Total height, h=7 m

Initial speed of second ball, u'=0

We have to find the height at which the two balls collide.

Let  first rubber ball and second ball strikes after t time.

For first ball

Distance traveled by first ball in time t

Substitute the value

  ...(1)

Distance traveled by second ball in time t

 .....(2)

Using equation (2) in equation (1) we get

sec

Now, using the value of t

S=6.17 m

Hence, at height 6.17 m the two balls collide .