We can use an equation to find the gravitational force exerted on the HST.
F = GMm / r^2
G is the gravitational constant
M is the mass of the Earth
m is the mass of the HST
r is the distance to the center of the Earth
This force F provides the centripetal force for the HST to move in a circle. The equation we use for circular motion is:
F = mv^2 / r
m is the mass of the HST
v is the tangential speed
r is the distance to the center of the Earth
Now we can equate these two equations to find v.
mv^2 / r = GMm / r^2
v^2 = GM / r
v = sqrt{GM / r }
v = sqrt{(6.67 x 10^{-11})(5.97 x 10^{24}) / 6,949,000 m}
v = 7570 m/s which is equal to 7.570 km/s
HST's tangential speed is 7570 m/s or 7.570 km/s
