By what factor does the kinetic energy of a car change when its speed is tripled?Multiple Choice: a) factor of 3 b) factor of 6 c) factor of 9 d)...

The correct answer here is C -- it increases by a factor of 9.  Here's why:

The formula for kinetic energy is

k = .5 mv^2 or k = .5*m*v*v

Where k is kinetic energy, m is the mass and v is the velocity.

If me assume that the mass of the car does not change as its speed changes, the only thing that changes is the velocity.

When the velocity triples, the kinetic energy goes up by a factor of 9 because the velocity gets squared while mass remains constant.