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Planet is orbiting a star

G = 6.67259 x 10^-11 Nm^2/kg^2

Mstar = 1.99 x 10^30 kg

mplanet = 5.98 x 10^24 kg

distance from perihelion to star = 1.69 x 10^11 m

distance from aphelion to star = 1.745 x 10^11 m

potential energy at perihelion = -4.698 x 10^33 J

Need:

Kinetic energy at perihelion

To solve for perihelion kinetic energy I used GMm/2r and checked it with -.5 x potential energy, but apparently this was incorrect as my answer (2.3493 x 10^33 J) was incorrect.

Am I missing something? Or could the "correct" answer be incorrect (this has been known to occur).

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# Homework Help: Orbital Energetics Help

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