Force on Rhonda's body from seat belt and windshield

[andthismeans]

Homework Statement

Rhonda, who has a mass of 60.0 kg, is riding at 25.0 m/s in her sports car when she suddenly slams on the brakes to avoid hitting a dog crossing the road. She is wearing her seat belt, which brings her body to a stop in 0.400s. What average force did the seat belt exert on her body? If she had not been wearing her seat belt, and the windshield had stopped her head in 1.0 X 10^-3s, what average force would the windshield have exerted on her?

Homework Equations

The only ones I know is P_i = P_f
[mv_1i + mv_2i = mv_1f + mv_2f] <---I don't know this as well
P = momentum i = initial f = final 1 = mass of first object 2 = mass of second object

The Attempt at a Solution

I don't know where force and time come in so I don't know how to start/finish it. Do I need another formula. If so, that's all the information I would need.

 

[LowlyPion]

Welcome to PF.

Consider that Force can also be expressed as the change in momentum (p) divided by the time over which it changes.

F = ma = Δp/Δt