Question

A ball is thrown vertically upward, which is the positive direction. A little later it returns to its point of release. The ball is in the air for a total time of 7.99 s. What is its initial velocity? Neglect air resistance.

Answer 1

v(t) = v(0) + ½ a t

Given:
g = -9.8m/s
t = 7.99s

Half way up the ball will reach 0 velocity.
0 = v + ¼ g t

Alternatively, all the way back, the ball will have a velocity equal but opposite to its initial.
-v = v + ½ g t

Use either equation to solve for v.

Answer 2

Correction:
use v(t) = v(0) + a t
v(½ t) = 0, so: 0 = v + ½ g t
v(t) = -v, so: -v = v + g t

Answer 3

ijiij

Answer 4

a