Question

Find the initial and final velocities in ft/s of a ball thrown vertically upward that returns to the thrower 3 s later ?

Answer 1

Given:

$t_{tot}=3\:\rm s$

The time of movement upward and downward is the same. Hence, the time of motion from initial point to the highest point is

$$t=t_{tot}/2=\rm 3\: s/2=1.5\: s$$

The initial speed of a ball

$$v_i=gt=9.8*1.5=14.7\:\rm m/s$$

The final speed is the same as initial

$$v_f=v_i=\rm 14.7\: m/s$$

In ft/s it's $48.2\:\rm ft/s$