Question

Two baseballs, each with a mass of 0.157 kg, are separated by a distance of 379 m in outer space, far from any other objects. If the balls are released from rest, what speed do they have when their separation has decreased to 173 m? Ignore the gravitational effects from any other objects.

What would the speed be, if the mass of the balls is quadrupled?

I tried using the equation v^2 = G M ((1 / R2) - (1 / R1)) and got the answer 2.07x10^-7 m/s, but the homework says that the answer is wrong.

Answer 1

PE2-PE1 = 2KE
G•m^2/r^2 - G•m^2/R^2 = 2•m•v^2/2.
v=sqrt[G•m•(R^2 - r^2)]/r•R =
= 1.66•10^-8 m/s

Answer 2

Its wrong.

Answer 3

v = sqrt(G*.157*((1/173) - (1/379))) = 1.81x10^-7 m/s

For the second question just multiply the mass by 4.
v= 3.63x10^-7 m/s