centripetal acceleration

[wood_magpies]

certain neutron stars rotate at about 1.0 revolutions per second. If such a star has a raduis of 20km, what minimum mass must it have so that material on its surface doesnt fly off during the rapid rotation?


ive tried working out the centripetal acceleration, being 7.89 X10^8
then subbed into the equation, assuming that m=1:
ive made m=the material on the surface and given it a value of 1
M= mass of neutron star
G= gravity constant = 6.674 x 10^-11

F = GMm/r^2


the answer i got turned out to be 4.7322 x10^24kg
but a few of my friends got 2.236x10^24 kg

can anyone help please?

[Filip Larsen]

With the given values, I get same result as you. You do seem to have a type in the magnitude of the centripetal acceleration, though.