Pre Calc Question

Question

A coin is dropped from the top of a 640 foot building. Its height relative to the ground is given by the function h(t)=−16t2+320. Answer the following questions rounding to two places where needed.

What is the height of the coin at 2 sec? 

ft.What is the height of the coin at 3.25sec? 

ft.At what time is the height of the coin 624 ft? 

sec.At what time is the height of the coin 100ft? 

sec.After 

sec the coin hits the ground. 

Answer 1

There is something wrong with this equation h(t) = -16t² + 320 because if you plug in t = 0 (the height of the coin prior to dropping it) you get the height of the coin = 320 and we are told the building is 640 feet tall.

If you had the correct equation, you just plug in t = 2 to find the height after 2 seconds, etc.

To find the time for a certain height, you let h(t) equal the height and solve the quadratic for "t" (probably using the quadratic formula).

Answer 2

Substitute 2 for t

Substitue 3.25 for t

Substitute 624 for h(t)

Substitute 100 for h(t)

Substitute 0 for h(t)