How do you calculate radial force?

Question

Just to qualify, I am given a radial acceleration.

If you are given the component of the acceleration in the radial direction, then you need to multiply that by the mass.

If you are given the time dependence of the coordinates, then you must first calculate the acceleration in the radial direction. E.g. in spherical coordinates the acceleration in the radial direction is:

d^2r/dt^2 - r (dtheta/dt)^2 -
r sin^2(theta)(dphi/dt)^2