How do I solve this Physics problem about an airplane dropping supplies

Question

A person in an airplane traveling 50 m/s to drop supplies to flood victims on an island 200m below. How many seconds before the plane is overhead should the supplies be dropped?

Answer 1

Compute the time to drop 200 m.

 

h = (1/2)gt²

 

2h/g = t²

√(2h/g) = t

√(2·200/9.8) = t

6.4 sec = t

 

It takes the supplies 6.4 sec to drop to the ground, so drop them 6.4 sec before you get directly overhead.