Recent content by Krappy

The total charge is finite if the charge for r>r0 is finite. That charge is given by Q(r>r0) = ∫ρ(r) dV = 4π∫ρ(r)r2 dr = 4πρ0r0n∫r2/rn dr Now you need to know for which values of n does the integral ∫1/rn-2 dr converges. (The integral being taken from r0 to infinity, obviously).

Hi tiny-tim! Thanks for answering. I was confused, because if I applied angular momentum conservation I would get a different result of applying linear momentum conservation. What I was missing and later found (which you confirmed) is that I couldn't apply the latter because I don't know the...

Bar collision with ground Homework Statement A uniform bar of mass m and length l has no angular velocity when the extremity A hits the ground without bouncing. If the angle α is 30º, what is the magnitude of v1, so that the bar rotates, around A, until it immobilizes on the vertical position...

Thank you Doc Al. I got confused since that with the last system I got the right answer. (Notice that if I substitute the equation T2-T1 = Ia/R^2 in the original second one, I get the same thing). The thing that I was missing in the first place was that both tensions were tangential to the...

I have though about this and I think that T1 must equal to T2 because, if not, the string would be extending. Am I thinking right? I ask this since before I though that it was the difference between the two tensions T1 and T2 that would accelerate the pulley, but now, I don't think that's the...

Because of the cross product. |r||F| * sin(x), but in that case, sin(x) is the cos(theta).

Homework Statement [PLAIN]http://img109.imageshack.us/img109/1267/picture2ae.png m_1 = 2kg m_2 = 6kg R = .25cm M = 10kg \theta = 30º \mu = 0.36 Find the acceleration of the system. Homework Equations The Attempt at a Solution m_1 a = T_1 - m_1 g \mu m_2 a = m_2 g \sin \theta - m_2 g \mu...

Homework Statement A block of wood, of side 2a and mass M is on an horizontal plane. When it turns, it does it over the edge AB. A bullet of mass m<<M and velocity v hits on the opposite face to ABCD, at a height of 4/3*a. The bullets gets stuck on the block. Find the minimum value of v so...

Thanks for answering. I know it's much better, but I'm solving some tests (same format) and the position in which this one appears is the "integration by parts question".

Homework Statement Calculate: \integral \frac{1}{(x^2+1)(x+1)} Homework Equations \integral f(x) g'(x) = f(x) g(x) - \integral f'(x) g(x) + C The Attempt at a Solution I've tried using both 1/(x+1) and 1/(x^2 + 1) as dv, but both end up in another integral I can't solve, one...

EDIT Should I assume that the force is always perpendicular to the vector that goes from the axis of symmetry to the point of contact between the rope and the body? Thanks for the answers.

Homework Statement We have a rigid body that is formed by two coaxial cylinders, one with radius r and another with radius R, r < R. There's a winding of string around the cylinder of smaller radius. The string is pulled with a constant force F making an angle \alpha with the horizontal...

Yes, sorry, I meant the same magnitude. Now I tried to solve this with using both Energy and Momentum conservation and it gave me something like 10^19 eV. But I think there's an easier way to solve it. Could you please post your resolution? Regards

Homework Statement An electron traveling at 0.8c annihilates with a positron that is at rest, producing two photons. One of the produced photons travels in the direction of the electron. Determine the energy of each of the photons.Homework Equations p_{photon} = \frac{E}{c} P_{electron} =...