Recent content by AndreAo

Thanks both! I did some mistakes. 1. p,q,r,s \inZ AlephZero, as you suggest, I think I should have said that p,q have no common factors, and r,s have no common factors, so they're reduced fractions. Until the point willem2 said, I think it's ok. Then 3(qs)^{2}\equiv0(mod 4). Thus, q or s...

Hi AlephZero, thanks for rewriting it. I'd like an opinion about the proof I did. First I proved, at least I think, that x^{2}\equiv0(mod 4) or x^{2}\equiv1(mod 4). Proof. Suppose x\inZ. Then either x is even or x is odd. We consider theses cases separately. Case 1: Suppose x is even...

Hello, I'm trying to do exercise number 20 from chapter 6 of this http://www.people.vcu.edu/~rhammack/BookOfProof/index.html, it asks to show that the curve x2 + y2 - 3 = 0 has no rational points. In the answer it has this tip: first show that a2 + b2 = 3c has no solutions, other than the...

Good sites, thanks!

I've found the solution for it, but I'll not reproduce in the answer: http://www.fisica.ufs.br/CorpoDocente/egsantana/ondas/interferencia/Interferencia.html , it's in portuguese. Thanks

I didn't draw it before, but I think this isn't the way to solve if a can find the locus of that points. Thanks for answering.

Homework Statement A line source of sound (for instance, a noisy freight train on a straight track) emits a cylindrical expanding sound wave. Assuming that the air absorbs no energy, find how (a) the intensity I and (b) the amplitude sm of the wave depends on the perpendicular distance r from...

Homework Statement Two point sources of sound waves of identical wavelength lambda and amplitude are separated by distance D = 2.0lambda. The sources are in phase. (a) How many points of maximum signal (constructive interference) lie along a large circle around the sources? (b) How many points...

The result before was: y(x,t)=a*sin(kx-wt)+b*cos(kx-wt) a*sin(kx-wt)+b*cos(kx-wt) = A sin(kx-wt+\beta) Applying the rule on the right side of equation: A[sin(kx-wt)*cos \beta+sin \beta*cos(kx-wt)] So, Acos \beta = a and Asin \beta = b A = a/cos \beta and A = b/sin \beta a/cos \beta =...

Thanks,I find the solution for that problem: Power = Force * Velocity Power = (-\tau*\partialy/\partialx)*\partialy/\partialt The negative it's because the force is contrary to the displacement?

Using just in sin(kx-wt+\phi): sin(kx-wt+\phi) = sin (kx-wt)*cos \phi+ sin(\phi)*cos (kx-wt) cos \phi = 0 sin \phi = 1 so sin(kx-wt+\phi) = cos (kx-wt). What is wrong?

Sorry, I researched a little and see that: P = Force x Velocity Using this formula and replacing the values I get the result

Yet in this exercise, it asks me what's the maximum power transferred along the string. I know the formula of kinetic energy, but I can't figure out what is the formula for potencial energy on this string. Do I have to first find this formula before calculating the max.value of power? How can I...

Thanks:smile: Using the principle of superposition: y(x,t)=a*sin(kx-wt)+b*sin(kx-wt+\varphi) Using sin(a+b)=sin a*cos b+sin b.cos a on the second sin of the expression above leads to: y(x,t)=a*sin(kx-wt)+b*cos(kx-wt) But I don't see a way to group sin and cos.

(a)The bar moves up and down 120 times per second, so the frequency f = 120 Hz. w = 2\pif replacing f = 120 Hz, w = 2*\pi*120 = 753,98 s^{-1}. How k = w/v and v = \sqrt{\frac{T}{\mu}} replacing the value of T = 90 N and \mu = 0,12 kg/m I received v = 27,39 m/s. k = 752,98/27,39 k = 27,49...