A fixed string in the third harmonic

[TFM]

Using:

v(x,t) = A_S_W \omega sin(\frac{\pi }{2}) cos(0)

gives me: 5.33

then

a(x,t) = A_S_W \omega ^2 sin(\frac{\pi }{2}) sin(\frac{\pi }{2})

gives me: 7700

Both of which are right. I disagree with mastering physics - if you diffentiate cos, it gives you minus sin:

a(x,t) = -A_S_W \omega ^2 sin(\frac{\pi }{2}) sin(\frac{\pi }{2}) giving -7700, which it said was wrong?

Many Thanks,

TFM

 

[Vuldoraq]

Indeed you do get minus sin, but -7700 would be the maximum deceleration, and it asks for the maximum acceleration. At least that's what I tell myself.

Thanks for your help with the period, I think I was having a mental bock.

 

[TFM]

Have you got the right answer yet for the time, as I have left the thread marked unsolved until you have finished.

I think I was having a mental bock.

Don't worry, I think it happens to all of us from time to time!

TFM

 

[Vuldoraq]

Yeah, I got in the end. Thanks for that .

By the way are you still working on the 'instantaneous power in a standing wave' problem? Sketching the graphs is quite tricky.