Force of Friction: Calculating Car's Acceleration

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Homework Help Overview

The discussion revolves around a physics problem involving a car's motion, specifically focusing on calculating the average force of friction acting on a car that is coasting to a stop after running out of gas. The subject area includes concepts of kinematics and dynamics.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the need to find the car's acceleration as a first step, with some suggesting using the change in speed over time. There is a question about how to relate the calculated acceleration to the force of friction.

Discussion Status

The discussion is active, with participants providing guidance on finding acceleration and relating it to the force of friction. There are multiple interpretations of how to approach the problem, and participants are exploring different aspects of the physics involved.

Contextual Notes

There is an emphasis on understanding the relationship between acceleration and force, with some participants questioning the initial conditions and the application of relevant equations.

elissadi
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I'm stuck! Please help! I have been looking @ this problem for 2 hours! :rolleyes:
A 1200 kg car has a speed of 30 m/s - it runs out of gas and coasts, stopping in 40 secs. What is average force of friction on the car?
Do you find the car's acceleration first? There is no force, so you can't use a=F/m
 
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You should be able to find the acceleration. Acceleration is the change of speed divided by the time taken. You know the time, how about the speed?
 
You get the acceleration by using the speed divided by 40 seconds.
 
Ok...

Ok, thanks...I found the acceleration, now how does that fit into the rest of the situation?
 
The friction force causes the acceleration of that mass (car). Use F = ma.
 
find the deceleration, then apply the eqn F=ma
 

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