What is the net force on the car?

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Homework Help Overview

The discussion revolves around a physics problem involving a car moving along a curved path, where participants are tasked with determining the net force acting on the car, specifically focusing on the static friction force as a fraction of its weight. The problem involves concepts from dynamics, including centripetal force and friction.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants explore the relationship between centripetal force and frictional force, with one participant attempting to equate these forces while questioning how to incorporate deceleration into the calculations. Others raise concerns about the vector nature of the forces involved, emphasizing the need to consider both tangential and radial components.

Discussion Status

The discussion is ongoing, with participants providing insights into the complexities of the problem. There is an acknowledgment of the need to analyze the vector components of the forces rather than simplifying the situation. No consensus has been reached yet, and various interpretations of the forces are being explored.

Contextual Notes

Participants are navigating the challenge of integrating the effects of deceleration with the centripetal force, highlighting the importance of understanding the directional nature of the forces involved. The problem is framed within the constraints of a homework assignment, which may limit the depth of exploration.

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Homework Statement


At a certain instant of time, a 1200 kg car traveling along a curve 250 m in radius is moving at a speed of 10 m/s but is slowing down at a rate of 2 m/s2. Ignoring air friction, what is the total static friction force on the car as a fraction of its weight at that instant?


Homework Equations


Fc = mv2/R
Ff = [tex]\mu[/tex]FN = [tex]\mu[/tex]mg


The Attempt at a Solution


I have an idea at how to attempt this...
mv2/R = Ff
(since the centripetal force is provided by the frictional force)
but I need clarification: I see it that the frictional force and the force due to the acceleration (deceleration) of the car act perpendicular to each other and therefore on different axes.
How would you account for this force due to deceleration in calculating the centripetal force? Is this just a matter of calculating the speed of the car at that instant, in which case the deceleration doesn't matter?
 
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Careful. Friction provides all the force accelerating the car, not just the centripetal force. There's both a tangential and a centripetal component.
 
Ah, okay. So the total frictional force is equal to mv^2/R - 2m = -1.6m?
 
Unfortunately it's not that simple.

The accelerations are vectors and they are not acting in the same direction.

Figure the sum of the vectors first because the slowing is tangential and the centripetal is radial.
 

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