Help with Free fall (physics)?

Question

I have no idea how to calculate free fall! What are the equations for it? And can somebody show me how to do these 2 equations:

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

You shoot an arrow straight up at 50m/s. When will it run out of speed.

Please help!

Answer 1

v = u + at is the basic equation for such problems where u is the initial velocity, a the acceleration, t the time and v the final velocity. Let us do the problems now.

v = 20 + 9.8 x 3 = 20 + 29.4 = 49.4 m/sec is the velocity in the first case.

Second case:

v = 0 when it stops.

so, 0 = 50 - 9.8t

t = 50 / 9.8

= 5.1 seconds