You are traveling at 40 m/s in a car whose mass (including you) is 8S0 kg When a

Question

You are traveling at 40 m/s in a car whose mass (including you) is 8S0 kg When a squirrel runs out onto the road you slam on your brakes skidding to a slop in 60 m. a) Use the work-kinetic energy theorem to calculate the work done by (energy dissipated by) friction DO NOT calculate the work directly using the integral definition. b) Assuming that the frictional force is a constant. DO use (lie integral expression 10 directly calculate the work done by (energy dissipated by) friction. c) How does the answer to b) change if you manage to slop in 50 m?

Explanation / Answer

given

vi =   40 m/s

vf = 0 m/s

m = 850 kg

d = 60 m

a) Workdone by friction = change in kinetic energy

= (1/2)*m*(vf^2 - vi^2)

= (1/2)*850*(0^2 - 40^2)

= -6.8*10^5 J <<<<<<<<<--------------Answer

b) Workdone = F.d

-6.8*10^5 = F*d*cos(180)

-6.8*10^5 = -F*60

==> F = 6.8*10^5/60

= 1.13*10^4 N <<<<<<<<<--------------Answer

c) Workdone = F.d

-6.8*10^5 = F*d*cos(180)

-6.8*10^5 = -F*60

==> F = 6.8*10^5/50

= 1.36*10^4 N <<<<<<<<<--------------Answer

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