Impulse imparted by the ground on the ball?

[jevillan]

Homework Statement

A mass 100.0 g is dropped from some height above the ground and rebounds to a point where it has 78% of its initial gravitational potential energy. As it hits the ground, it is moving at 1.2 m/s. What is the impulse imparted by the ground on the ball?

Homework Equations

impulse = m(vf-vi)

The Attempt at a Solution

impulse = (0.1)(1.2 m/s - 0 m/s)
=0.12 kg m/s

I followed the formula for impulse, but i feel like I did it wrong because there was a lot more information given in the problem that I didn't use in my solution

 

[bob1182006]

I think you need to take into account the ball's velocity after colliding with the ground.
Also you're saying vf = 1.2m/s but the problem states that vi = 1.2m/s.
To find vf you need to use the information about the gravitational potential energy.