For a steel alloy it has been determined that a carburizing heat treatment of 4-h duration will raise the carbon concentration to 0.38 wt% at a point 3.4 mm from the surface. Estimate the time (in h) necessary to achieve the same concentration at a 6.8 mm position for an identical steel and at the same carburizing temperature.

Asolid cylinder is concentric with a straight pipe. the cylinder is 0.5 m long and has an outside diameter of 8 cm. the pipe has an inside diameter of 8.5 cm. the annulus between the cylinder ad the pipe contains stationary oil. the oil has a specific gravity of 0.92 and a kinematic viscosity of 5.57 x 10-4 m2/s. most nearly, what is the force needed to move the cylinder along the pipe at a constant velocity of 1 m/s?