Finding the Work Done by Friction w/out Friction

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SUMMARY

The discussion revolves around calculating the work done by friction for an 80-kg baseball player sliding to a stop after running at 6.5 m/s. The correct calculation of work done by friction is determined to be approximately -1700 J, contrasting with the initial incorrect calculation of -169 J. The key equations used include W = ΔK and W = F * d, with the friction force being derived from the coefficient of kinetic friction (μ) and the normal force (N).

PREREQUISITES
  • Understanding of kinetic energy calculations (ΔK = 1/2mv^2)
  • Familiarity with the work-energy principle (W = F * d)
  • Knowledge of friction concepts, specifically coefficient of kinetic friction (μ)
  • Basic algebra skills for arithmetic verification
NEXT STEPS
  • Study the derivation of the work-energy principle in physics
  • Learn about the calculation of friction forces and coefficients in real-world scenarios
  • Explore advanced topics in energy conservation and transformation
  • Practice problems involving work done by friction in various contexts
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Students studying physics, particularly those focusing on mechanics, as well as educators looking for examples of work-energy problems involving friction.

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I feel like I'm missing some obvious or simple piece but I can't seem to figure out the first part. If I can get the first part, the second part is easy.

1. Homework Statement

An 80-kg baseball player running at 6.5 m/s goes into a slide 3.0 m from second base. He comes to rest just as he touches the bag. What is the work done by friction? What is the coefficient of kinetic friction between the player and the ground?

Homework Equations


W = F * d
W = ΔK
F = μN

The Attempt at a Solution


This seemed straight forward. I calculated the kinetic energy to get the overall work:
W = Kf - Ki = 1/2mv_f^2 - 1/2mv_i^2 = -169 J
This should be the same work as the friction but I've been told the correct answer should be -1700 J. Am I wrong about something here?
 
Last edited:
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Check your arithmetic.
 
Bystander said:
Check your arithmetic.

m = 80kg
v_i = 6.5m/s
v_f = 0

1/2(80)(0)^2 - 1/2(80)(6.5)^2 =
0 - 1/2(80)(42.25) =
0 - 1/2(338) =
0 - 169 = -169

Same answer.
 
Check it again --- it's glaring at me with big red eyes.
 
Wow! How did I miss that twice!

1/2(80)(0)^2 - 1/2(80)(6.5)^2 =
0 - 1/2(80)(42.25) =
0 - 1/2(3380) =
0 - 1690 = -1690 ≈ -1700
 

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