Only 8.1 seconds before the bus crashed into the lunar surface at a speed of 2,900 meters per second (6,500 miles per hour), the radar altimeter would generate a fusing signal at an altitude of 21.4 kilometers (13.3 miles). At that moment, bolt cutters would free the hard lander and retrorocket from the bus. A three nozzle spin motor would fire, lifting the package 0.8 meters (2.5 feet) above the bus and imparting a spin of 300 RPM. The retrorocket would then fire, slowing the capsule to a virtual stop at a height of only 335 meters (1,100 feet) above the lunar surface. Explosive bolts would cut the clamp holding the lander to its retrorocket and the two would be separated by springs. The hard lander would then free fall to the surface with an impact speed of 45 meters per second (100 miles per hour), give or take 9 meters per second (20 miles per hour).
That's why math and science are cool, kids.