Hydraulic Piston on te bottom of a hill

[jenha14]

At a ride in an amusement part a cart, with a mass of 150 kg, rolls down a long curved hill. The height of the hill is 50 m and the length of the track that the cart follows is 300 m. As the cart rolls down the hill, it experiences both a rolling frictional force and air resistance. The net effect of these two resistive forces over the run is equivalent to a constant force of 70 N, which is opposite to the cart's velocity.
(A) If the cart starts out at rest at the top of the hill, what is the speed at the bottom?
(B) There is a large hydraulic piston at the bottom of the hill thate engages the cart and brings it to rest by applying a force for 5.0 m. Neglecting all other resitive forces, what is the magnitude of the force needed to stop the cart?

relevant EQUATIONS

(Uf - Ui) + (Kf - Ki) = -Fd

ATTEMPT AT THE SOLUTION

I found (A) to be 26.4 m/s, but I have no idea on where to start on part (B)

 

[Doc Al]

I found (A) to be 26.4 m/s,

Looks good.

but I have no idea on where to start on part (B)

You can solve part (B) in any of several ways. You can use energy methods: How much work is required to bring it to rest? Or you can use kinematics: What acceleration is needed to bring it to rest in the given distance?