I'm struggling. A ball is thrown downward with an initial speed of 20 m/s. I need to calculate the time required to reach a speed of 50 m/s. Can you help?

Yup, you need to know your kinematics formulae well and that would be a piece of cake :)

Use

V being the final velocity, u the initial velocity, a the acceleration due to gravity and t the time elapsed between the final and initial speed. Give it a try, and post the answer :)

-50 m/s = -20m/s + (-9.8m/s/s x t)
t = 3.06s

Well done! :)

You see, it's easy!