Question

If a curve with a radius of 88m is perfectly banked for a car traveling 75km/h, what must be the coefficient of static friction for a car not to skid when traveling at 95km/h? ac=v^2/r

Answer 1

I wonder, if the track is perfectly banked, why do we need friction.. When the track is banked, it is not the friction which provides centripetal force.. It's a component of normal force which provides the centripetal force.. So, do we need friction.. I guess no..
Lets suppose a condition when track is not banked, we need friction but it is the kinetic friction which we need.. Static friction has nothing to do when the car is not in motion..

Conclusion: this question seems absolutely absurd to me. If there's an answer, it must be zero.

Answer 2

lol it's got me completely confused too, but thats physics in general :/

Answer 3

@ujjwal
Sorry, this is not absurd. The bank angle is only 'perfect' for vehicles travelling a specific speed.

Any other speed might cause the vehicle to skid inwards or outwards if friction is not enough.

@Jscaptrsn
You have to draw a picture of the bank with the body on it and draw all forces acting on it.
Then use the fact that the body is in a steady circular motion to apply N's 2nd law.

Answer 4

yeah, sorry. I didn't read the question properly..
But @Vincent-Lyon.Fr still what has static friction got to do in this case.. The car is in motion. So, it should be kinetic friction, isn't it?

Answer 5

2 possible answers:
- the car is moving in one direction (along the curve), but is NOT skidding in the perpendicular direction. Simple but not too accurate.
- it is not stated in the wording of the question but the wheels of the car must be rolling without slipping, so actually pure static friction applies. Correct explanation.

Answer 6

you mean to say rolling friction is equal to static friction?

Answer 7

Rolling friction is actually something else (represented by a torque).

But, true, when a body is rolling on a support or base, there is no slipping so friction (friction represented by a force associated to normal force) is static.