Which force is the ramp supporting the car

Question

Four forces contribute to the net force on a car on a rolling ramp

Answer 1

Hailey,

Probably nobody's answered this for you yet, because the data and question are both a little unclear!

Is the car rolling down a (stationary) ramp, or is the ramp rolling (for reasons best known to it!)? And, if the car is rolling, is it rolling freely (without interference by power provided by the car's engine, by engine resistance (if it's in gear) or by braking or other frictional forces)? And lastly, usually cars rolling down ramps roll with their tires turning (i.e., rolling instead of skidding). Plus which, should you be considering wind resistance? All of these factors contribute to the question of where you should look for forces.

Now, depending on the level of your course, you may already know how to "decompose" the force of gravity into pieces that are parallel and perpendicular to the plane of the ramp. And, you may know that the ramp is only responsible for counteracting the force acting perpendicular to it (the 'normal' force). So that's either 2 or 3 forces. Assuming it counts as 2 (decomposing the gravity into pieces doesn't make it into different forces, really; it's just something we do so that we can mathematically understand what parts of it function in different ways), then next the tires provide a special resistance to the acceleration of the car down the ramp: they have a moment of angular inertia which appears as a resistance to spinning faster -- hence, as a frictional force to brake the car, right where they contact the ramp. And lastly, the wind resistance acts to push the car back up the ramp, acting on a point somewhere on the front of the car (exactly where, determined by the design of the body. Hopefully, wind resistance and aerodynamic lift do not make the car go airborne as it rolls down!).

If you can think of any other likely force candidates, add them to the list. Of course, the major forces are gravity and the support force of the ramp; the tire rotational inertia won't matter a lot unless it's a monster truck with huge, heavy tires, and the wind effects won't matter until the car really gets going (they tend to scale as the square of the wind speed. That's why cars generally get the best gas mileage around 50 mph -- faster than that the wind dominates, and slower than that, the internal friction or inefficiency of the engine dominates.

Happy rolling!

Answer 2

Forces acting on the car on a rolling ramp
 
1. component of the wt of the car draging car down the ramp. = mgsinθ, theta is the angl of the ramp surface with horizontal.
2. component of the wt of the car acting perpendicular to the surface ( = mgcosθ) of the ramp will be counter balanced by the reaction of the ramp surface on the car.
3. Force of friction acting against the motion. = μ.mgcosθ, μ is coefficient of friction between car and ramp.
 
If force of friction = component of wt dowm the ramp, car will be stationary.
:)