Is the Laser-Induced Motion in SHM or Mechanics?

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Homework Help Overview

The discussion revolves around a problem that appears to involve mechanics and possibly simple harmonic motion (SHM) in the context of laser-induced motion. The original poster is trying to understand how a laser affects a mass suspended from a string, particularly in relation to Maxwell's Equations.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster considers the direction of the laser's force on the mass and its implications for motion, questioning whether it leads to SHM or a different mechanical scenario. They express uncertainty about the amplitude and frequency due to missing information about the string length. Other participants suggest using conservation of mechanical energy to find the maximum height instead of focusing on amplitude.

Discussion Status

Participants are exploring different interpretations of the problem, with some guidance provided on using conservation of energy. There is no explicit consensus on the approach, but the discussion is moving towards clarifying the relationship between energy input and the resulting motion.

Contextual Notes

The original poster notes that the problem does not provide the length of the string, which complicates their calculations for frequency and amplitude. There is also a mention of the energy input being relatively small compared to the expected motion, raising questions about the assumptions made regarding the laser's effect.

Jack_O
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I am struggling with the following question:

homeworkex2.jpg


My attempt so far is:

homeworkex2attempt.jpg

(in the diagram h is supposed to be A)
(i have also assumed the pulse time is negligible, so the mass starts at the resultant velocity)

The set of homework questions this has come from is supposed to be related to Maxwell's Equations but this one seems to have become a mechanics problem. After reading the question i first thought that the laser would be pushing the mass directly upward against gravity, but after calculating the resultant velocity and re-reading the question my best guess is that it's supposed to be pushing the mass horizontally while it is suspended from a string.

This would be SHM i thought and the amplitude would be the height increase. My problem now is the problem doesn't give the length of the sting and i can't find a way to calculate f or A without using l.

Any help much appreciated.
 
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The question doesn't ask for the amplitude of the oscillation. It's only asks for the maximum height. Use conservation of mechanical energy.
 
OK, i was barking up the wrong tree, after equating E(p) and E(k) i got h=v2/(2g), after plugging in the values i got about 2.3x10^-4m. This seems quite small for a 200J energy input but i guess it's reasonable as the force light exerts is minuscule?
 
That seems right. 200J/c isn't going to be much momentum.
 
Ok, thanks.
 

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