A fast-moving car carries much more destructive potential in a crash than a slow-moving one because its kinetic energy increases with the square of its speed.

When a net force acts on an object, it does work on the object, changing its velocity and consequently its kinetic energy according to the work-energy theorem. The energy is directly proportional to the mass and the square of the velocity, meaning doubling the velocity quadruples the kinetic energy.

Pay close attention to whether speed or velocity is squared in mechanical formulas, as missing the exponent or the fraction $\frac{1}{2}$ is a frequent source of negative marks in competitive exams.