45. Jeff Gordon (a race-car driver) discovers that he can accelerate at 4.0 m/s^

Question

45. Jeff Gordon (a race-car driver) discovers that he can accelerate at 4.0 m/s^2 without spinning his tires, but if he tries to accelerate more rapidly, he always "burns rubber."
(a) Find the coefficient of friction between his tires and the road. Assume the force from the engine is applied to only the two rear tires.
(b) Have you calculated the coefficient of static friction or kinetic friction?

67. A bullet of mass 10 g leaves the barrel of a rifle at 300 m/s. Assuming the force on the bullet is constant while it is in the barrel, find the magnitude of this force. Hint: Start by estimating the length of the barrel.

Explanation / Answer

Normal reaction on each tire = N =mg/4

Now only two tire are used for acceleration => max force available = N + N = 2N

Now we know that max accelaration = 4 => max force = ma = 4m

2N = 4m

=> 2mg = 4m => = 2/g

Since the tire are not slipping till this instant the coffecient is of static friction.

67)For this question assume the accelartion to be a. if the length of barrel is l

we have

v2=u2 + 2al

=> a = v2/2l

Once you know a use newtons 3rd law of equal and oppostie reaction to find the force on gun that will be equal to that on bullet

Force on bullet = m*a = .01 * 3002/2l = 450/l N

I leave estimating the barrel length to you

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