Verified answer

A 1498 kg car has a speed of 13.4 m/s when it hits a tree. The tree doesn’t move and the car comes to rest.?

Find the change in kinetic energy of the car.

Answer in units of J

Initial KE = ½ * mass * velocity^2 = ½ * 1489 * 13.4^2

Find the amount of work done by the car as

its front is pushed in.

Answer in units of J

As the car’s front is pushed in, the velocity of the car decreases from 13.4 m/s to 0 m/s. So, as the car’s front is pushed in, the kinetic energy decreases from the initial KE to 0 Joules.

During the collision, the tree exerts the force which causes the car’s velocity to decrease to 0 m/s.

The work done by the tree, as car’s front is pushed in, is equal to decrease of kinetic energy of the car.

Work = Initial KE = ½ * 1489 * 13.4^2

Find the magnitude of the force that pushed the front of the car in by 55 cm.

Work = average force * distance; distance = 55 cm = 0.55 meter.

½ * 1489 * 13.4^2 = average force * 0.55

Average force = (½ * 1489 * 13.4^2) ÷ 0.55

This is correct, except the answer to the first and second question is negative because of (KEf-KEi), and since KEf=0, when you subtract the answer you get from the work you do for the equation of the first question, you will get a negative answer for both the first and second questions.