The lens labelled (A) has radii 16.3cm and 11.6cm. Using the shape of the lens to assign the signs of the radii, calculate the focal length of the lens. Give your answer with the correct positive or negative sign using the usual convention for lenses.

The space between two 15-in.-long concentric cylinders is filled with glycerin (viscosity = 8.5 × 10-3 lb·s/ft2). the inner cylinder has a radius of 1 in. and the gap width between cylinders is 0.1 in. determine (a) the torque and (b) the power required to rotate the inner cylinder at 180 rev/min. the outer cylinder is fixed. assume the velocity distribution in the gap to be linear.