# Physics

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A 4.00 103-kg car has a speed of 9 m/s. The car then hits a tree. The tree doesn't move and the car comes to rest.
(a) Find the change in kinetic energy of the car.
. J
(b) Find the amount of work done in pushing in the front of the car.
J
(c) Find the size of the force that pushed the front of the car in 50 cm.

- i got -2.00e+05 for the first answer and -4.00e+05 for the third, but neither worked?

• Physics -

ΔKE =KE2 – KE1 = 0 - m•v²/2 =
= 4000• 9² /2 = - 162000 J.
a =v² /2•s =9² /2• 0.5= 81 m/s²
F =ma =4000•81 = 324 000 N

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