[tex]\pi[/tex]Hi everyone,(adsbygoogle = window.adsbygoogle || []).push({});

I hope you can help me out with the following question. I am mainly confused about the sign

1. The problem statement, all variables and given/known data

A block in SHM with T= 4.0 s and A=0.1 m. How long does it take the object to move from x=0 m to x= 0.06 m.

2. Relevant equations

x=Acos(wt + [tex]\phi[/tex])

w=2pi/T

where T is period, w is angular frequency, phi is phase angle and A is amplitude.

3. The attempt at a solution

Using eq2, i solved for w, wich is [tex]\pi[/tex]/2.

Then I set eq1 equal to 0. The value of phi is thus + or - [tex]\pi[/tex]/2. Since the object is assumed to be moving to the right (as it would have to if it wants to go from 0 to 0.06 m),. then we take the negative phase angle. Then, back to eq1, I put

0.06=0.1cos(([tex]\pi[/tex]/2)t - [tex]\pi[/tex]/2)

NOW, this is were my problem is.

Apparently, there are then two possible answers,

either 0.927 = ([tex]\pi[/tex]/2)t - [tex]\pi[/tex]/2, which gives 1.59 s

or - 0.927 = ([tex]\pi[/tex]/2)t - [tex]\pi[/tex]/2. which gives 0.41 s

Firstly, I dont understand when are we supposed to have a + and - option. Secondly, I dont trust the answer given, which is 0.41 s. Please help.

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# Homework Help: Simple harmonic motion - please help

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