One easy physics problem. Need in one hour!!

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1a) Assume that all the mass of a galaxy is in a massive uniform density ball of stars (called bulge by astronomers), with a radius of 1 kpc. The total mass of this bulge is 3 × 1010 M⊙ The volume of a sphere with radius R is: 4/3πR3 . Calculate the rotation speed at the center, at 0.5 kpc at 1 kpc, at 2 kpc, 4 kpc, and 8 kpc from the center of this galaxy. Express the velocities in km/s and make a drawing of the rotation curve.