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## Homework Statement

Sputnik I was launched into orbit around Earth in 1957. It had a perigee (the closest approach to

Earth, measured from Earth's center) of 6.81 × 10

^{6}m and an apogee (the furthest point from

Earth's center) of 7.53 × 10

^{6}m. What was its speed when it was at its perigee? The mass of Earth

is 5.97 × 10

^{24}kg and G = 6.67 × 10

^{- 11}N ∙ m

^{2}/kg

^{2}

## Homework Equations

F=GMm/r

^{2}F=mv

^{2}/r

## The Attempt at a Solution

I tried to use the formula above which is GM/r=v

^{2}, however I substituted both 6.81x10

^{6},7.53x10

^{6}and took the average of two of them , the answer still did not match with the MC answer which is 7840m/s

I am curious about what should be the radius, and actually the orbit is not a perfect circle with a perigee and an apogee , is it acceptable to use the equation in circular motion . Thank you.