On an icy winter day, the coefficient of friction between the tires of a car and a roadway is reduced to 2/3 its value on a dry day. As a result, the maximum speed vmax dry at which the car can safely negotiate a curve of radius R is reduced. The new value for this speed is what percentage of its value on a dry day?

Question

ljetibo · Answer

You start by setting up the system on a normal day. What are all the forces acting on the car in a turn? Draw a diagram. One of the forces involved will have speed in it.
Express that speed over other quantities. It doesn't matter that you don't know how much they are. Five, Seven and a quarter... whatever. Just use letters for them.

Write that same equation for speed, but substitute the letter you used to mark the friction coefficient in the first equation with 2/3*letter you used to mark the friction coefficient in the first equation.

Divide the first and second gotten equations. Everything you don't know the value of should pretty much cancel out and you will be left with just a single number.