physics
posted by janie .
An astronaut exploring a distant solar system lands on an unnamed planet with a radius of 2520 km. When the astronaut jumps upward with an initial speed of 2.94 m/s, she rises to a height of 0.83 m. What is the mass of the planet?

Calculate the value of the acceleration of gravity "g" on that planet using
V = sqrt(2gH), which leads to
g = V^2/(2H)
Then use g = GM/R^2 to solve for the planet mass, M. G is the universal constant of gravity and R is the planet's radius 
unfortunately those calculations didn't work, its saying my answer varies significantally