Question

A girl throws a tennis ball straight into the air with a velocity of 64 feet/sec. If acceleration due to gravity is -32 ft/sec2, how many seconds after it leaves the girl's hand will it take the ball to reach its highest point? Assume the position at time t = 0 is 0 feet.

4 secs
2 secs
1 sec
Cannot be determined

Answer 1

the height y is given by
y = -16t^2+64t
as with all y=ax^2+bx+c
the vertex (max in this case) is at -b/2a = 2

Answer 2

change in up velocity/time = -32 ft/s / s
original up velocity = 64
so when will the velocity up be zero???

v up = 64 - 32 t
0 = 64 - 32 t
t = 2 sconds

Answer 3

Thank you