# Search results

1. ### Pion decay in QED

Hi, I was wondering whether the decay of the Pi-0 meson in QED to an electron positron pair can occur as follows: Pi-0 -> virtual photon -> e+e- or does it have to go via Pi-0 -> two virtual photons -> e+e- (the Feynman diagram has a 'square' of virtual electrons/photons)? I have...
2. ### Particle exchange and parity

I'm struggling with the relation between particle exchange and parity with the case of para- and ortho-hydrogen. The overall wavefunction must be antisymmetric with respect to particle exchange and so for para-hydrogen (an antisymmetric spin state) the spatial part of the wavefunction must be...
3. ### Components of 4-momentum

Firstly, apologies for the notation. The 4-momentum of a massive particle (rest mass m) is defined by p=mu where u is the 4-velocity. Thus in a frame S in which a particle has 3-velocity u the components of p are [p]=gamma*(mc,mu) How can we then identify the zeroth component of...
4. ### Conservation of angular momentum of a falling particle

Homework Statement A stone is dropped from a stationary helicopter 500m above the ground, at the equator. How far from the point vertically below the helicopter does it land? Homework Equations Conversation of AM The Attempt at a Solution Let the height above the ground it is...
5. ### Rocket Equation with varying gravity

So, the rocket equation is F_ext = m(dv/dt) + u(dm/dt) where m is the mass of the rocket, v the velocity, u the effective exhaust gases speed, and F_ext the external forces on the system. If we take a constant mass ejection rate p, and take the external force to be the gravitational...
6. ### How do you write in scientific notation ?

How do you write in scientific notation "the (SI) units of x are..."? For example, the SI units of time are seconds. Is there any succinct way I can write this? Maybe it's like this: {time} = s ?
7. ### Gauss's Law

Hi, can you derive Gauss's Law without using Coulomb's Law? If so, how? Thanks
8. ### Rotational acceleration

I'm getting confused with different types of acceleration when dealing with rotating systems. There is centripetal acceleration, tangential acceleration, and angular acceleration as far as i know. How do you derive that linear momentum equals angular momentum multiplied by the radius? And...