Chapter 6, Problem 3MCP

A frictional force f provides the centripetal force as a car goes around an unbanked curve of radius R at speed V. Later, the car encounters a similar curve, except of radius 2R, and the driver continues around this curve at the same speed V. In order to make this second curve, the frictional force on the car must be equal to

1. A.    2f.
2. B.     f.
3. C.     $\frac{1}{2}f$.
4. D.    $\frac{1}{4}f$.