Question

2. An object is launched straight up. The object attains a height of 107 m after 2.50 s.
a. What was the initial velocity?
b. When (i.e. how long after launch) will the object have a speed of 20 m/s on the
way back down?

Answer 1

I have answer to the first question. i am not sure about second, how do you get the time.

Answer 2

use Vf = Vi -a*t
-20 = (whatever you found for Vi) -9.8*t
solve for t