how to solve a second order - vector deferential equation using ode45

Hi, I need to solve the following ode using ode45 (in order to find a sattelite's orbit):

r''=-(mu/norm(r)^3)*r

where mu is a known constant and r is a 3*1 column vector I have initial conditions for both r and r', and I want to find r and r' for a certain time interval. The thing is I can't figure out the syntax to accomplish it. Your help would be greatly appreciated