Kinetic Friction of moving car hitting a stationary car

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SUMMARY

The discussion centers on calculating the initial speed of a moving car that collided with a stationary car, given a skid mark length of 47 meters and a coefficient of kinetic friction of 0.68. The user initially calculated an acceleration of 6.66 m/s² and derived an initial velocity of 86.81 km/h using the kinematic equation Vx² = Vox² + 2ax(deltax). However, this result was incorrect, prompting a suggestion to apply the conservation of energy principle, where the work done by friction equals the change in kinetic energy of the car.

PREREQUISITES
  • Understanding of Newton's second law (F=ma)
  • Familiarity with kinematic equations, specifically Vx² = Vox² + 2ax(deltax)
  • Knowledge of the concept of kinetic friction and its coefficient
  • Basic principles of energy conservation in physics
NEXT STEPS
  • Study the conservation of energy in the context of frictional forces
  • Learn how to calculate work done by friction using Wf = ukN
  • Explore advanced kinematic equations and their applications in real-world scenarios
  • Review the relationship between speed, acceleration, and distance in collision analysis
USEFUL FOR

This discussion is beneficial for physics students, automotive engineers, and accident reconstruction specialists who require a deeper understanding of motion dynamics and collision analysis.

orange03
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Homework Statement


A police officer investigating an accident estimates from the damage done that a moving car hit a stationary car at 24 km/h. If the moving car left skid marks 47 m long, and if the coefficient of kinetic friction is 0.68, what was the initial speed of the moving car? (The answer is in km/h.)


Homework Equations



F=ma
Vx^2=Vox^2+2ax(deltax)



The Attempt at a Solution



I found acceleration by putting uk(mg)=max. I got 6.66 m/s^2 for acceleration. I plugged it into the kinematic equation Vx^2=Vox^2+2ax(deltax) and got 24.11 m/s for initial velocity. Then, I converted it into km/h and got 86.81 km/h. But, the answer is wrong and I don't know how to do it the correct way.
 
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I'd use conservation of energy.

Work done by friction = change in kinetic energy of the car

Wf=ukN
 

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