A ball is thrown straight down with an initial speed of 20m/s. After 3 seconds, how fast is it going?

Question

I got an answer of 50 m/s (from another online source)

but need a formula to achieve the answer above

please help :(

Answer 1

With down being the positive direction, 

 

v(t) = v_o + gt

 

v(t) = (20 + 9.8t) m/s,

 

with t in seconds.

 

v(3) = [20 + 9.8(3)] m/s = 49.4 m/s

 

Your online source must have been using a value of 10 m/s² for g, which is a rough approximation, though convenient if you do not have a calculator.