Car Speed Ratio Question

[courtney1121]

Estimate the ratio of the forces required to keep your car at a speed of 75 mph to that required to keep your car at a speed of 65 mph. What impact does this have on your gas mileage?

Where should I start?

[courtney1121]

OK so you will have a force of gravity, normal force, drag, and static friction. Gravity will be down, normal will be up, drag will be towards the left and static friction will be towards the right since they are trying to keep the car at a certain speed.

So where to go from here?