P$4$ A horizontal true centrifugal casting process is used to make brass bushings with the following

dimensions: length $=10cm,$ outside diameter $=15cm,$ and inside diameter $=12cm.($a$)$ Determine

the required rotational speed in order to obtain a G$-$factor of $70.($b$)$ When operating at this speed,

what is the centrifugal force per square meter $(Pa)$ imposed by the molten metal on the inside wall

of the mold?