Two crates, A and B, sit at rest side by side on a frictionless horizontal surface. The crates have masses mA and mB. A horizontal force F is applied to crate A and the two crates move off to the right. Draw the free-body diagram for crates A and B.

Engines for propeller-driven aircraft are limited in their maximum rotational speed by the fact that the tip speed of the propeller must not approach the speed of sound in air (mach i). taking 6 ft as a typical diameter for a propeller of a light airplane and 1100 fils as the speed of sound, find the upper limit on the rpm (revolutions per minute) of the propeller shaft.