We have a balanced positive-sequence threephase source for which van(t) = 150 cos(400πt + 15◦) v a. find the frequency of this source in hz. b. give expressions for vbn(t) and vcn(t). c. repeat part (b) for a negative-sequence source.

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?