A my diver jumped from an airplane. He used his watch to time the length of his jump. His height above the ground can be modelled by h= -5(t-4)^2+2500, where h is his height above the ground in meters and t is time in seconds from when he started his timer.

Question

A my diver jumped from an airplane. He used his watch to time the length of his jump. His height above the ground can be modelled by h= -5(t-4)^2+2500, where h is his height above the ground in meters and t is time in seconds from when he started his timer. 
a) how long did the sky diver delay his jump? I got about 26 seconds by setting h=0. But the textbook answer is 4 seconds.
B) from what height did he jump? I got 2420 by setting t=0. But the textbook answer is 2500

Steve · Accepted Answer

since (t-4), he delayed 4 seconds The timer started at t=0. His dive time is t-4. at t=4, he jumped. plug in t=4, and you are left with 2500.