How to solve??? please!!

The ratio of the inner diameter to the outer diameter ratio of a shaft at 0.6. determine the appropriate diameters for this requirement if required 1.5 MW at 220 rpm provided the maximum shear stress can not be used 56 MPa.

This is important 1. what happens to the speed of molecules in water vapor when it condenses to form a liquid? (2 points) the molecules slow down. the molecules speed up. the molecules slow down and then speed up. the molecules speed up and then slow down. 2. how might human activities change to compensate for a decrease in water supplies? (2 points) humans might build a factory. humans might build drainage systems. humans might extract more water from the ground. human behavior does not change because of the water cycle. i'll be grateful if anyone can answer these 2 questions !