1. A ball is dropped from a cliff 50 m high. a) With what velocity does it hit the ground? B) How long is the ball in the air?

 a) Isolate the givens

vo = 0
a=g =-9.8 m/s^2
x = -50 m

Find v

 

 g points down; is negative
x points down; is negative

Of the two solutions possible, the negative solution is correct.. The ball is moving downward when it hits the ground.

 b)

vo =0
x = -50m
a = g =-9.8 m/s^2

Find t

 
  time is a scalar and as such can only be positive or zero; it can never be negative or imaginary