Question

Calculate the force of gravity on a spacecraft 19200 km (3 earth radii) above the Earth's surface if its mass is 1600 kg.

Hint: At three earth radii from the surface of the Earth, the gravity force (weight) of the spacecraft will be reduced to
(1/4)^2 = 1/16 of the weight when the spacecraft is at the Earth's surface, since it is 4 times farther from the Earth's center.

(1/16) x M g = ?

g is the value at the Earth's surface, 9.8 m/s^2. M = 1600 kg.

Answer 1

9040

Answer 2

Simply use Newton's law of Universal Gravitation, FG = G*(m1m2)/r^2 where G = 6.67e-11 N*m^2/kg^2
Using this we get (6.67e-11)*((1600kg)(5.98e24kg))/(19200km*1000)^2
which should give you: 1730N of force. The most common mistake to make for this problem is forgetting to convert the distance from km to m.

Answer 3

Correct