Two balls are dropped to the ground from different heights. One ball is dropped 2s after the other, but both strike the ground at the same time 5s after the Ist is dropped.
(a) What is the difference in the heights from which they were dropped ?
(b) From what height was the first ball dropped?

Explanation

(a)For the first ball s=`h_(1)`,v=0,t=5 sec
`s=ut+(1)/(2)at^(2),h_(1)=0xx5+(1)/(2)9.8xx5^(2)=122.5m`
For the second ball s=`h_(2)`,u=0,t=3 sec `therefore h_(2)(1)/(2) "gt"^(2)=(1)/(2)xx9.8xx9=4.9xx9=44.1m`
Difference in heights `h=h_(2)-h_(t)=122.5-44.1=78.4m`
(b)The first ball was dropped from a height of `h_(1)`=122.5m.