A ball is dropped from an elevator at an altitude of `200 m` (Fig.4. 39). How much time will the ball take to reach the ground if the elevatior is
.
a. Stationary?
b. Ascending with velocity `10 m s^(-1)`
c. Descending with velocity `10 m s^(-1)?

Explanation

a. `s=ut+(1)/(2)at^(2) rArr -200=0 xx+(1)/(2) (-10)t^(2)`
`rArr t=sqrt40 s`
b. `-200=10t-(1)/(2) t^(2)`
`rArr t^(2)-2t-40=0 rArr t=1+sqrt41 s`
c. `-200=-10t-(1)/(2) 10t^(2) rArr t^(2)+2t-40=0`
`rArr t=-t+ sqrt41 s`.