The net force acting on a car rolling down a ramp is the addition of two forces...?

Question

a) Name the 2 forces on the car
b) Name the 2 forces that help the car
b) Name the 2 forces that oppose the force

Answer 1

Assume the ramp makes an angle th with respect to horizontal.

a) The two forces acting on the car are gravity and kinetic friction

b) The two forces that help the car are the component of gravity which is parallel to the ramp. This is:
Fgp=sin(th)*m*g

Since the car is moving, it has momentum. So there is essentially a force which is counter acting the kinetic friction. The way to conceptualize this force is to consider what would happen if the car rolled onto a horizontal surface off the ramp. It would not stop immediately. The kinetic energy of the car would get converted into heat through friction. This force would be the force of friction offset by the acceleration or deceleration of the car.

c) The opposing force is friction. The two forces will be the air resistance since the car is moving through air which requires work to displace. The other force is the friction in the bearings of the various moving parts of the car.

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Answer 2

Gravity and Inertia I thought about this. If you have a free falling object, you know how fast it gains momentum, and it will continue to gain that momentum unless slowed by friction. If there is no friction then the car would continue to accelerate at the rate of wich an object picks up speed due to the gravitational pull of the earth.