Question

a kid with a baseball cap is playing catch with himself by trowing a ball straight up how fastdoes he throw the ball if it comes back to his cap in0.8 seconds later

Answer 1

Since it went up and came down, we know that it fell for .4 seconds.

s = 1/2 a t^2 = 16 * .016 = .256 feet

v = Vo - at
0 = Vo - 32 * .4 = Vo - 12.8
Vo = 12.8 ft/s

Double check:

s = 12.8t - 16t^2
= t(12.8-16t)
has zeros at t=0, 0.8

Wow - some arm that guy has, eh? Threw the ball 3" up!