How Is Force Calculated in a Tennis Serve?

[AnomalyCoder]

Homework Statement

A tennis player returns a 30m/s serve back at 25 m/s after making contact with the ball for .5 seconds. If the ball has a mass of .20kg, what is the force exerted on the ball?

Homework Equations

I = Force$$\Delta$$Time, or essentially the $$\Delta$$Momentum = Impulse
P=M*V

The Attempt at a Solution

Before: .2kg object traveling at -30m/s.
After: .2kg object traveling at 25m/s.

Yeah I'm lost. Not quite sure how to handle this.
How do I apply .5s?

 

[SammyS]

Homework Statement

A tennis player returns a 30m/s serve back at 25 m/s after making contact with the ball for .5 seconds. If the ball has a mass of .20kg, what is the force exerted on the ball?

Homework Equations

I = Force$$\Delta$$Time, or essentially the $$\Delta$$Momentum = Impulse
P=M*V

The Attempt at a Solution

Before: .2kg object traveling at -30m/s.
After: .2kg object traveling at 25m/s.

Yeah I'm lost. Not quite sure how to handle this.
How do I apply .5s?

0.5 s = Δtime
What was the change in momentum?

 

[AnomalyCoder]

Well, since momentum = mass * velocity...
The change in mass is none, since the ball doesn't change in terms of its mass?

Then if velocity = distance/time...
First it's -30m/s, goes to 25m/s...
-5m/s in velocity?

But that would mean the change in momentum is 0..
I think I messed up somewhere.

 

[SammyS]

The difference between -30m/s and 25m/s is 55 m/s, not 5 m/s.

25m/s - (-30m/s) = 55 m/s.

Also, m·25m/s - m·(-30m/s) = m·55 m/s ≠ 0.

Usually m doesn't change.