Finding friction coefficient, car unbanked curve.

[blee2x2]

Homework Statement

What is the minimum coefficient of friction needed between the tires and the ground so you make the turn safely?[/B]

Car= 1394.7kg
You=75kg
Radius of turn = 40m
Velocity = 20m/s

Homework Equations

Fnet = MAc (Ac = centripetal Acceleration) = Force of friction
Force of Friction (Ff) = Mu(Fn) of Mu(mg)
MAc = (MV^2)/r[/B]

The Attempt at a Solution

(MV^2)/r = Mu(Mg) mass cancels out and i solve for mu ==> mu = (V^2/rg)

mu = 20^2 / (40*9.8)= 1.02

If that is correct is it possible for the friction coefficient to be more than 1?

 

[ehild]

Homework Statement

What is the minimum coefficient of friction needed between the tires and the ground so you make the turn safely?[/B]

Car= 1394.7kg
You=75kg
Radius of turn = 40m
Velocity = 20m/s

Homework Equations

Fnet = MAc (Ac = centripetal Acceleration) = Force of friction
Force of Friction (Ff) = Mu(Fn) of Mu(mg)
MAc = (MV^2)/r[/B]

The Attempt at a Solution

(MV^2)/r = Mu(Mg) mass cancels out and i solve for mu ==> mu = (V^2/rg)

mu = 20^2 / (40*9.8)= 1.02

If that is correct is it possible for the friction coefficient to be more than 1?

Yes, it can be between the tyre and the asphalt.

 

[blee2x2]

So since the Friction coefficient is more than 1... that just means it is stronger than the normal force? but is that the minimum?

 

[ehild]

So since the Friction coefficient is more than 1... that just means it is stronger than the normal force? but is that the minimum?

What is minimum? The maximum of the static friction is μmg. Now μ is slightly greater than one. Imagine the tyre is sticky, you put some glue on it. In that case the "force of friction", the contact force between the tyre and asphalt can be quite big.You can find μ-s greater than 1 in this table. http://www.engineeringtoolbox.com/friction-coefficients-d_778.html
μ>1 means that you need greater force to pull the body on the horizontal force than to lift it vertically.