Finding the Work Done by Friction w/out Friction

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Homework Help Overview

The problem involves calculating the work done by friction on a baseball player sliding to a stop after running. The subject area pertains to mechanics, specifically work-energy principles and friction.

Discussion Character

  • Exploratory, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to calculate the work done by friction using kinetic energy changes but arrives at a different value than expected. Participants question the arithmetic and encourage re-evaluation of the calculations.

Discussion Status

Participants are actively engaging in checking the calculations presented by the original poster. There is a focus on verifying the arithmetic involved in the work-energy equation, with some guidance offered to reassess the computations.

Contextual Notes

There appears to be confusion regarding the expected result for the work done by friction, with the original poster initially calculating -169 J and later adjusting to -1690 J, which is approximated to -1700 J. The discussion highlights the importance of accuracy in calculations.

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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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