posted by tatiana .
I had wrote that was because I was told that in the beginning of the spring being wound the PE=KE.
Can I check a concept question, The amount of work required to stop a moving object would be equal to the mass of the object times it intial speed due to mv^2 right. You need to apply the same kinetic energy to stop.
THe work done on a brake in stopping (force*distance) will be equal to the change in KE.
The homework question asks: which work woulf be required to stop a moving object: the intial speed, the intial kinetic energy of the object, the mass of the object times it acceleration, the mass of the object times its intials speed, or the square of the intial speed of the object.
Since you said its based on change in KE, The work required to stop the car would be intial KE