Is Mass Irrelevant in This Problem?

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SUMMARY

The discussion centers on the relevance of mass in solving a kinematics problem involving an automobile sliding to a stop. The problem states that the car's wheels are locked at an initial speed of 34.9 m/s with a coefficient of kinetic friction of 0.266. Participants clarify that mass is not necessary to determine the stopping time, as the equations of motion can be solved without it. The key takeaway is that mass does not influence the time taken to stop in this specific scenario, emphasizing the importance of symbolic reasoning over numerical computation.

PREREQUISITES
  • Understanding of kinematic equations
  • Knowledge of Newton's second law (F=ma)
  • Familiarity with the concept of friction and its coefficients
  • Ability to perform dimensional analysis
NEXT STEPS
  • Study the derivation of kinematic equations without mass dependency
  • Learn about the implications of friction coefficients in motion problems
  • Explore dimensional analysis techniques in physics
  • Investigate the role of mass in other physics problems
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Students studying physics, educators teaching kinematics, and anyone interested in understanding the principles of motion and friction in real-world scenarios.

Arwing
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Homework Statement
An automobile's wheels are locked as it slides to a stop from 34.9 m/s. If the coefficient of kinetic friction is 0.266 and the road is horizontal, how long does it take the car to stop?
Relevant Equations
F=ma, Fg=mg, Fk=coefficient of friction * Fn
I'm not sure where to start, I feel like I'm missing the mass but it is not listed.
 
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Maybe you don't need the mass. What do the kinematic equations that don't depend on mass have to say?
 
Arwing said:
Homework Statement:: An automobile's wheels are locked as it slides to a stop from 34.9 m/s. If the coefficient of kinetic friction is 0.266 and the road is horizontal, how long does it take the car to stop?
Relevant Equations:: F=ma, Fg=mg, Fk=coefficient of friction * Fn

I'm not sure where to start, I feel like I'm missing the mass but it is not listed.
You don't need the mass. Go ahead and solve the equations to find the acceleration.
 
Arwing said:
Homework Statement:: An automobile's wheels are locked as it slides to a stop from 34.9 m/s. If the coefficient of kinetic friction is 0.266 and the road is horizontal, how long does it take the car to stop?
Relevant Equations:: F=ma, Fg=mg, Fk=coefficient of friction * Fn

I'm not sure where to start, I feel like I'm missing the mass but it is not listed.
You could assume a) it's a toy car with a mass of ##1 kg##; and, b) a real car with a mass of ##1000 kg##; and see what difference that makes.

Which car will stop quicker? The toy or the real one?
 
This thread highlights a common bad habit among many students: trying to compute every single partial result numerically. Most of the time it will be more illuminating to make general symbolic considerations for general input parameters and only insert particular values given in the problem once a general expression for the final result has been reached.

If you think mass is relevant, then introduce a mass parameter m and see if it appears in the final result.
 
Addendum: It can be argued on dimensional grounds that the mass is necessarily irrelevant in this problem.
 

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