Question

I just can't get around physics T^T this is the last question i promise, I'd really appreciate the help <3

question; the work one by friction force to stop a car of mass 1000 kg moves with velocity 72km/h is ..........

a) 72 x 10³ J

b) 2 x 10⁴ J

c) 2 x 10⁵ J

d) 4 x 10⁵ J

an explanation for future reference would be great, thank you in advance!
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Answer 1

Use the work-energy theorem. The total work W performed on the car as it it slows to a stop is equal to the change in the car's kinetic energy ∆K. So

W = ∆K

W = 0 - 1/2 (1000 kg) (72 km/h)²

W = - (500 kg) (20 m/s)²

W = - 200,000 J = -2 × 10⁵ J

The closest answer would be C, but friction opposes the car's motion so the work would be negative.