Estimate the gravitational force exerted by a shuttle on Earth.
When the space shuttle (mass of the shuttle=2*10^6kg) was at the outer limit of Earth's atmosphere (distance= 350km above Earth's surface), astronauts measured the gravitational force from Earth to be equal to 1.7*10^7 newtons. Assuming that both Earth and the shuttle are point masses, calculate the gravitational force of Earth on the shuttle when the shuttle was at the limit of the mesosphere, i.e., at 90km from Earth's surface. Also, what is the gravitational force the shuttle exerts on Earth at this point?