Angular momentum and tension of string

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Discussion Overview

The discussion revolves around a physics problem involving a puck revolving in a circle on a frictionless table, focusing on the calculation of tension in the string based on given angular momentum and radius.

Discussion Character

  • Homework-related

Main Points Raised

  • A participant presents a calculation for the tension in the string based on angular momentum, using the formula L = mrv and subsequently calculating velocity and force.
  • Another participant points out a potential error in the radius used in the calculations, suggesting that the radius should be 0.50 m instead of 0.25 m.
  • A third participant agrees with the correction regarding the radius, emphasizing that the string represents the radius of the circular motion.
  • A fourth participant admonishes the original poster for double posting, directing them to a previous thread.

Areas of Agreement / Disagreement

There is disagreement regarding the correct radius to use in the calculations, with some participants asserting that the radius is 0.50 m while the original poster used 0.25 m. The discussion remains unresolved as to the correct tension calculation based on this disagreement.

Contextual Notes

The original calculation depends on the assumption of the radius, which affects the resulting tension. The discussion does not resolve the implications of this assumption on the final answer.

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This problem is baffling me.

A 3kg puck revolves in a circle on a frictionless table at the end of a 50cm long string. The puck's angular momentum is 3kg (m^2/s). What is the tension in the string?

This what I did
L= mrv
therefore
3kg*.25m*v = 3kgm^2/2
v=4m/s
F=(mv^2)/r
(3kg*16m/s)/(.25m) = 192N

is this right?
 
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r should be 0.50 m, not 0.25.
 
I agree with arildno, the string is acting as the radius of the circle itself, not as the diameter :smile:
 

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