Find the magnitude and direction of the net gravitational force on mass A due to masses B and C in Fig. E13.6
. Each mass is 2.00 kg.

 Two spheres are separated by 10m. If the lighter 40kg sphere feels a gravitational force of 1.6 × 10^-9 N, what is the mass of the heavier sphere?

(II) You are explaining to friends why an astronaut feels weightless orbiting the Earth in a space station, and they respond that they thought gravity was just a lot weaker up there. Convince them that it isn’t so by calculating how much weaker (in %) gravity is 380 km above the Earth’s surface.