Question about friction? Dynamics

[Ricardeo Xavier]

Homework Statement

This is the problem
http://imgur.com/a/1XFlt

2. Homework Equations
This is the given FBD
http://imgur.com/a/CURqA

3. The Attempt at a Solution
Now the car should have a tendency to slip down the ramp thus causing the frictional force to oppose this motion. But the frictional force is pointed down the ramp in this worked out problem. Can someone explain to me why this is?

 

[Ricardeo Xavier]

Why is friction pointed down the ramp? Shouldnt it be pointed up the ramp?

 

[Chestermiller]

If there were no ramp (i.e. the ground was flat) and the car was going around a curve, what direction would the friction force have to point?

 

[Doc Al]

Why is friction pointed down the ramp? Shouldnt it be pointed up the ramp?

Note that they ask for minimum and maximum speeds. What happens when you take the curve too fast? Which direction do you tend to slip?

 

[kuruman]

Why is friction pointed down the ramp? Shouldnt it be pointed up the ramp?

Follow the sequence of the questions asked by the problem.
First draw the FBD to determine how fast the car must be moving if there were no friction, i.e. sliding around a frictionless curve.
If the car is moving faster than that, friction down the incline is needed to keep it in a horizontal circle.
If the car is moving slower than that, friction up the incline is needed to keep it in a horizontal circle.

 

[Ricardeo Xavier]

Thanks everyone for the great responses! It really helped clarify things for me (: