Astronauts on the ISS orbit Earth 16 times a day at a height of 400km above the surface. Given that the radius of Earth is approximately 6400km, how fast are the astronauts travelling?

v = 2𝜋R/T where R is the orbital radius, T is the time period.R = radius_of_earth + height_of_orbit = 6800km + 400km = 6800km = 6.8×10⁶m.T = hours_in_day/number_of_orbits_in_day = 24/16 hours = 1.5 hours = 90 minutes = 5400 seconds.v = (2𝜋×6.8×10⁶)/5400 ≈ 7900ms^-1.For appreciation of how fast this is, this corresponds to around 18000mph, which is 10 times the speed of an average bullet, and over 20 times the speed of sound in air!