Impulse of a falling ball under gravity onto a solid surface

[GatorJ]

Homework Statement

A 0.5-kg rubber ball is dropped from rest a height of 19.6 m above the surface of the Earth. It strikes the sidewalk below
and rebounds up to a maximum height of 4.9 m. What is the magnitude of the impulse due to the collision with the sidewalk?

Homework Equations

J=\DeltaP

The Attempt at a Solution

mgh=.5mv²
v=\sqrt{}2gh

Just before collision:
v=\sqrt{}2*9.8*19.6
v=19.6 m/s

Just after collision:
v=\sqrt{}2*9.8*4.9
v=9.8 m/s

J=m(v_after-v_before)=.5(9.8-19.6)=4.9 kg m/s

The answer is 14.7 N.s, so I'm not sure what I'm missing.

 

[aim1732]

Well velocity is a vector - is this how you would subtract them?

 

[GatorJ]

J=.5[9.8-(-19.6)]=14.7 kg m/s

Wow that was a stupid mistake, thanks!