Rotational Motion maximum speed

[physgrl]

Homework Statement

3. A 1500 kg car is moving on an un-banked curve with a radius of 98 m. The coefficients of static and kinetic friction are 0.73 and 0.50 respectively. The maximum speed the car can move without skidding is:

*a. 27 m/s

b. 22.4m/s

c. 21 m/s

d. 30 m/s

e. none of the above

Homework Equations

Fn*μ=mv²/r

The Attempt at a Solution

I used that formula with the coefficient of kinetic friction (because the object is in motion when it has velocity) and I got 21.9...the answer key says its 27.

 

[LawrenceC]

Have you tried using static friction? Until the vehicle begins drifting, you only have static friction. At every instant in time, the rubber that is in contact with the road surface is not moving relative to the road surface. It's called the instantaneous center.

 

[Andrew Mason]

I used that formula with the coefficient of kinetic friction (because the object is in motion when it has velocity) and I got 21.9...the answer key says its 27.

If the car is not sliding sideways, you would use the coefficient of static friction. The static friction force is perpendicular to the direction of motion at all times.

AM

 

[physgrl]

Ohhh got it i was thinking about friction in the other direction. Thanks

 

[asteriatic]

As a scientist, it is important to always check your calculations and assumptions when solving a problem. In this case, it seems that you may have used the incorrect coefficient of friction. The problem states that the car is moving on an un-banked curve, which means that the coefficient of static friction should be used. Using this coefficient, the maximum speed the car can move without skidding is indeed 27 m/s, which is the correct answer provided in the options. It is always important to pay attention to details and use the correct equations and values in order to obtain accurate results in scientific problems.