Simple Harmonic Motion question.

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Homework Help Overview

The discussion revolves around a problem involving two simple pendulums of different lengths (0.40 m and 0.60 m) and their oscillation periods. Participants are tasked with determining when the pendulums will be in sync again and how many oscillations each pendulum completes during that time, using the formula for the period of a pendulum.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss calculating the period of each pendulum and express confusion about the next steps after finding the periods. There are questions about the meaning of "set off oscillating in step" and whether the pendulums are coupled or separate. Some participants also share hints regarding the relationship between time and the number of oscillations.

Discussion Status

There is ongoing exploration of the problem, with some participants sharing their calculations and others questioning the assumptions made about the pendulums' synchronization. Hints have been provided, but there is no explicit consensus on the interpretation of the results or the reasoning behind certain steps.

Contextual Notes

Participants note constraints related to homework rules that prevent step-by-step guidance. There is also mention of rounding answers to significant figures, which raises further questions about the implications for synchronization of the pendulums.

gabloammar
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Homework Statement


Two simple pendulums of length 0.40 m and 0.60 m are set off oscillating in step. Calculate (a) after what further time the two pendulums will once again be in step, (b) the number of oscillations made by each pendulum during this time. (Assume g = 10 ms-2

Homework Equations



T = 2[itex]\pi\sqrt{l/g}[/itex]

The Attempt at a Solution



I get the two different values for T, but I'm stuck after that. I've got the solution with me but I need someone to explain getting the answer to me step by step I suppose. If anyone needs the solution I'd be happy to type it all out. Thanks!
 
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Yes, what is your actual attempt at the solution? We can show you the next step with it.
 
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No see MY attempt at the solution was finding T first, and after that I'm stuck. What I said above is that I've got the solution written with me in the textbook and that if you need the whole solution to tell me what's happening then I'll gladly type it all out or scan it in a while and post it here and maybe then you can help me. However it suits you :)
 
what does it mean by 'set off oscillating in step'? Are these coupled or separate pendulums? If they are separate, then it seems like a sort of trick question...
 
gabloammar said:

Homework Statement


Two simple pendulums of length 0.40 m and 0.60 m are set off oscillating in step. Calculate (a) after what further time the two pendulums will once again be in step, (b) the number of oscillations made by each pendulum during this time. (Assume g = 10 ms-2


Homework Equations



T = 2[itex]\pi\sqrt{l/g}[/itex]

The Attempt at a Solution



I get the two different values for T, but I'm stuck after that. I've got the solution with me but I need someone to explain getting the answer to me step by step I suppose. If anyone needs the solution I'd be happy to type it all out. Thanks!

Sorry, can't do the step by step, it's against board rules. But I'll give you a big hint:

The number of cycles an oscillator has gone through after time [itex]t[/itex] can be represented by [itex]\frac{t}{T}[/itex], where [itex]T[/itex] is the period. If this number is an integer, it means it's undergone that many complete oscillations within that time. If the number is not an integer, it means that it is in the "middle" of an oscillation at the time.

To be in sync, two oscillators which have been synchronised at the start need to have a cycle number difference which is a whole number. The smallest integer is zero (this occurs at the start). The next integer is one.

Can you work out the solution now?
 
Curious3141 said:
Sorry, can't do the step by step, it's against board rules. But I'll give you a big hint:

The number of cycles an oscillator has gone through after time [itex]t[/itex] can be represented by [itex]\frac{t}{T}[/itex], where [itex]T[/itex] is the period. If this number is an integer, it means it's undergone that many complete oscillations within that time. If the number is not an integer, it means that it is in the "middle" of an oscillation at the time.

To be in sync, two oscillators which have been synchronised at the start need to have a cycle number difference which is a whole number. The smallest integer is zero (this occurs at the start). The next integer is one.

Can you work out the solution now?

[Sorry just read the rules again, didn't read 'em that well before I suppose. But I understand why you can't help me step by step and that's fine since it's the rules.]

Secondly, YES! See I've got the solution and everything but I didn't understand why we needed to take the second oscillation as (n-1), I understand the rest of it. Was just stuck at this part. Thank you SO much!
 
what answer did you arrive at?
 
For (a), I got 6.86 s. And for (b), the shorter pendulum makes 5.5 oscillations and the longer pendulum makes 4.5 oscillations :)
 
And this is the same as the answer given in the textbook? Strictly speaking, the two are not exactly in step again. But they are close to being in step.
 
  • #10
Yep, 'cause I got to round 'em off to two significant figures.
 
  • #11
But what did you round off to two significant figures? the number of oscillations? So the number of oscillations shouldn't be 5.5 and 4.5 ? But then they would not be in sync.

I guess I'm trying to argue with the textbook's answer. And you've probably moved on from this question a long time ago. So don't worry about it.
 

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