Physics Question from TBR (Work and Energy)

[SeeEll]

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The problem is as follows:

The toy car, after attaining a maximum speed, skids to a stop on a rough section of the surface. Which of the following quantities must be measured in order to calculate the length of the skid?

I. The mass of the car
II. The coefficient of kinetic friction between the road and the wheels
III. The initial speed of the car

Answer is II and III.

I thought it would be I, II, and III because of the following.

W=FD = 1/2mv2 - 1/2mv2 - (kinetic friction)(normal force)

I solved for D to get the distance of the skid and found that mass, velocity initial, and friction were all relevant parts of the equation. My explanation is a bit sparse, but could anyone shed some light on my situation?

 

[BerkReviewTeach]

The problem is as follows:

The toy car, after attaining a maximum speed, skids to a stop on a rough section of the surface. Which of the following quantities must be measured in order to calculate the length of the skid?

I. The mass of the car
II. The coefficient of kinetic friction between the road and the wheels
III. The initial speed of the car

Answer is II and III.

I thought it would be I, II, and III because of the following.

W=FD = 1/2mv2 - 1/2mv2 - (kinetic friction)(normal force)

I solved for D to get the distance of the skid and found that mass, velocity initial, and friction were all relevant parts of the equation. My explanation is a bit sparse, but could anyone shed some light on my situation?

You have the right idea, but need to cancel some things out.

Start with:

Work = deltaKE

mukinetic x N x dskid = 0 - 1/2mvinitial^2​

Because N = mg, we get:

mukineticmg x dskid = - 1/2mvinitial^2​

The mass of the car cancels out, and leaves you with the distance depending on mukinetic, g, and vinitial.

 

[SeeEll]

Thank you for your explanation.