Question

The mass of car 2 is twice the mass of car 1. If both cars have the same velocity, how does the kinetic energy of car 2 compare to car 1?

Car 2 has four times the kinetic energy.
Car 2 has twice the kinetic energy.
Both cars have the same kinetic energy.
Both cars increase in kinetic energy if they slow down.

Answer 1

Car 2 has twice the kinetic energy.

Reason: K = 1/2 m v^2. With v the same and m2 = 2 m1, K2 = 1/2 (2 m1) v^2 = 2(1/2 m1 v^2) = 2 K1.