Recent content by Dovahkiin

I knew I would have missed something simple ;) Thanks!

Homework Statement I am struggling to calculate the gravitational force from a dark matter halo given that its density is given by ρ(r) = ρ0r02/r2. Once i have found the force i plan to equate it to the centripetal force, F = mv2/r, to find the velocity, v. Homework Equations Density...

I don't seem to be able to edit my OP anymore, but I've realized i haven't fully defined all the variables (units in brackets): . N is the number of particles remaining after the foil . N0 is the starting number of particles . x is thickness (m) . n is number of nuclei per unit volume...

Homework Statement In an experiment carried out with a beam of thermal neutrons it is found that on traversing a 2mm thick foil of 197Au, some 70% of the neutrons are removed. What is the total thermal neutron cross-section for this isotope of gold? (Density of gold: 19300 kg m-3) Homework...

Yes, the way i think of it is as almost an equation in itself as this means you can handle the units algebraically and include any factors of magnitude (such as kilo).

Well you know the quasars velocity relative to the Earth and you know the protons velocity relative to the earth. So you know the protons velocity in the Earths rest frame, and you can lorentz transform it into the quasar rest frame using the quasar velocity. Don't forget the signs of the...