Verified answer

The car is going at a constant speed, and the hill angle is constant also. So the momentum does not change. The rate of change of the momentum is zero.

If mass, speed and direction remain constant; then the rate of change of momentum is zero.

Rate of change of momentum is a fancy way of saying a force:

F= ma = (mv - mu) / t

Assuming no friction and no thrust of the car. The force downhill will be mgsin(5).

Since you have no mass you can't work out the force.