Which can cause physical weathering of rock?

A acid
B oxygen
C sun
D wind

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.

Which of the following is tru about semi-conductors

Acircuit contain a 5-ohm,a3-ohm,and an 8-ohm resistor in series. what is the total resistance of the circuit ?