If a ball is thrown upwards at 20 ft/sec, the height h after t seconds is given by h = -16t2+ 20t.

How many seconds does it take for the ball to reach its maximum height, and what is this height?

A. time = 5/16 seconds
height = 5 and 1/8 feet

B. time = - 5/8 seconds
height = 6 and 1/4 feet

C. time = 5/8 seconds
height = 6 and 1/4 feet

D. time = - 5/16 seconds
height = 5 and 1/8 feet

Question

If a ball is thrown upwards at 20 ft/sec, the height h after t seconds is given by h = -16t2+ 20t. 

How many seconds does it take for the ball to reach its maximum height, and what is this height?

A. time = 5/16 seconds 
height = 5 and 1/8 feet	

B. time = - 5/8 seconds 
height = 6 and 1/4 feet	

C. time = 5/8 seconds 
height = 6 and 1/4 feet	

D. time = - 5/16 seconds 
height = 5 and 1/8 feet

myininaya · Answer

So we have
$$h(t)=-16t^2+20t$$
This is a parabola that looks like this $$\cap$$

|dw:1339367992031:dw|

Find the vertex of the parabola and you will find the highest point.

So write $$h=-16t^2+20t$$
in the following form:
$$h=a(t-m)^2+n$$
Where (m,n) is the vertex
and m is the time while n is the height at that time.