Finding forces on a car rounding a curve

[baird.lindsay]

Homework Statement

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.

Homework Equations

F=ma
mv^2/r

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.

 

[mfb]

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.

 

[haruspex]

arctan ∅ \frac{40^2}{-9.8m/s*80}
I get theta 1.11° degrees but that seems kindsa low.

No, 1.11 radians.