Hi everyone. I just finished 2 questions but I'm not sure if the answer is right. So can anyone help me check it?(adsbygoogle = window.adsbygoogle || []).push({});

The first question is:

"Police find the tire tracks of a car that lost control and caused an accident. They want to know if the car was speeding. They determine that μs=0.65 for it's tire on this road. The tire marks are 126m long. How fast was the car traveling?"

Answer:

Fcar(the force of the car)

Fcar= μsFn Fn=mg

Fcar= μsmg

Fcar=ma

ma=μsmg

cross out the m

a=μsg

a=0.65*9.8

=6.37m/s^2

d=vt

t=v/a

d=v*(v/a)

126=v^2/6.37

v=28m/s

The velocity of the car was 28m/s

The second question is "Calculate the force acting on the body of a 60kg person who is involved in an accident. His car hits a tree while going 15m/s. The car comes to a stop with the tree embedded 1.1m into it."

Answer:

t=d/v

=1.1m / 15m/s

=0.07s

a=v/t

a=15m/s / 0.07s

=214m/s^2

Fbrake(The force of the break)

Fbrake=ma

=60*214

=12840N

So the force acted upon the person is 12840N

I'm not really sure of question 2's answer cause it seems a bit too big.

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# Homework Help: Physics Friction question

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