Hi everyone. I just finished 2 questions and corrected some mistakes 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[backward]

V2^2=V1^2+2ad

0=v1^2+(2*6.37*126)

v1=40m/s

So the car was travelling 40m/s before it crashed

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:

v2^2=v1^2+2ad

0=15^2+2a*1.1

2.2a=225

a=102m/s^2[backward]

Fbrake(the force of the brake)

Fbrake=ma

=60*102

=6240N

So the force acted upon the person is 6240N

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# Revised Friction Question

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