The gravitational constant should have units m^3/kg/s^2 not m^3/kg/s. This will asure that v_earth will have a unit of m/s. To transform this unit to km/h you have to multiply by 3.6. This gives us a speed of 40'255 km/h. I cant't figure out where the 671 km/h comes from.

Regards, daCake

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