Physics Problem Kinetic Energy

Question

Starting from rest, you drive down a street, when accelerating from 15 mph to 30 mph, your change in kinetic energy is ________ our change in kinetic energy from

0 mph to 15 mph.

A)One third

B) One half

C) Equal to

D) Two times

E) Three times

I do not understand why the answer is E. Can someone explain? Using the KE=1/2mv^2 equation.

Answer 1

The change in KE from 15 to 30 mph is 1/2m(30)² - 1/2m(15)² = 900/2m - 225/2m = 675/2m

The change in KE from 0 to 15 mph is 1/2m(15)² - 1/2m(0)² = 225/2m - 0 = 225/2m

(675/2m)/(225/2m) = 675/225 = 3