# Homework Help: Finding forces on a car rounding a curve

1. Feb 21, 2013

### baird.lindsay

1. The problem statement, all variables and given/known data
A car with mass of 1200kg turns sharply with a radius of 40m and at 15/ms. The tires have a static friction of 0.9, rolling at 0.6 and kinetic at 0.3.

1) how long does it take to make a turn at half a circle.
2) what is the magnitude of frictional force on the tires in the turn
3) After the turn, the car accelerates to 40m/s, assuming the divers uses max acceleration from friction, how long does it take to reach the new speed.
4) the driver takes another curve at 40 m/s with a radius of 80 and skids. the roads are banked. what angles does the road need to be banked to prevent skidding.

2. Relevant equations
F=ma
mv^2/r

3. The attempt at a solution

a) t=$\frac{2\Pi R}{v}$= $\frac{2 Pi (40)}{15}$ so 16.75 seconds

b) F=ma
F$_{smax}=$1200$\frac{v^2}{r}$
F$_{smax}=$1200$\frac{15^2}{40}$
=6750N
c) have no clue how to do C....im not sure how to go about it...

D) arctan ∅= $\frac{v^2}{gR}$

arctan ∅ $\frac{40^2}{-9.8m/s*80}$

I get theta 1.11° degrees but that seems kindsa low.

Last edited: Feb 21, 2013
2. Feb 21, 2013

### Staff: Mentor

1/a: half a circle, not a full circle.
2/b: I agree
3/c: Given the coefficient of friction, what is the maximal horizontal force between car and ground?
4/d: Did you draw a sketch?

In general, keeping the units everywhere can help to spot mistakes.

3. Feb 21, 2013