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## Homework Statement

a) Calculate the mas of a proton ( ms = 1.67 * 10^-27 kg) whose kenetic energy is half its toral energy. (ANS. 3.34 * 10^ -27 kg)

b) How fast is it travelling? ( ANS. 0.87c) c- speed of light

## Homework Equations

E(kenetic) = Gm(1)m(2) all over R^2

E(total) = -0.5Gm(1)m(2) all over R

V(orbit) = sqrt. GM/r, where M is the mass of planetary object

E = mc^2

## The Attempt at a Solution

The most I can come up with is that there is no gravitational potential energy because

1/2E(k) = E(total)