Runner A & B Paths Cross: Displacement of B from Flagpole

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Discussion Overview

The discussion revolves around a problem involving two runners, A and B, who are moving towards each other from opposite sides of a flagpole. The focus is on determining the displacement of runner B from the flagpole at the moment their paths cross. The context includes elements of kinematics and relative motion.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • Runner A is initially 4.54 miles west of the flagpole and runs east at 7.06 mi/h, while runner B starts 4.34 miles east and runs west at 6.82 mi/h.
  • One participant calculated that runner A will take approximately 0.643 hours to reach the flagpole, while runner B will take about 0.636 hours, suggesting they will cross near the flagpole.
  • Another participant suggested writing the displacement of each runner as a function of time to find the crossing point, indicating a method to solve the problem.
  • Questions were raised about the initial distance between the runners and their relative velocity, with a suggestion to divide the distance by the relative velocity to find the crossing time.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the exact displacement of runner B at the crossing point, and the discussion includes various approaches and calculations that remain unresolved.

Contextual Notes

There are missing assumptions regarding the exact moment of crossing and the implications of the calculated times. The discussion does not clarify the method for determining the displacement at the crossing point.

AdnamaLeigh
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Runner A is initially 4.54 mi West of a flagpole and is running with a constant velocity of 7.06 mi/h due East. Runner B is initially 4.34 mi East of the flagpole and is running with a constant velocity of 6.82 mi/h due West. Consider East to be in the positive direction. What is the displacement of runner B from the flagpole when their paths cross? Answer in units of mi.

Thanks.
 
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Please show how you started, and where you got stuck.
 
I figured out that it will take A .643hr to reach the flagpole but B .636hr so I know that when the two cross, it's going to be on the left side of the pole, with negative displacement. At .636hrs, A will be 0.05mi away from the pole so they should cross soon. That's where I'm stuck; I think I'm making this too confusing.
 
You should try to write down the displacement of each runner as a function of time, like this:

[tex]x(t)=vt+x_0[/tex],

where [itex]x(t)[/itex] is the displacement, [itex]v[/itex] is the velocity, [itex]t[/itex] is the time, and [itex]x_0[/itex] is the initial displacement. To find out when the runners meet, simply equate the two functions and solve for time.
 
What is the initial distance between the two runners?
What is their relative velocity?
Dividing the distance by the velocity you find the time they take to cross each other.
 

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