An experimental engine weighing 480 lb is mounted on a test stand with spring mounts at...

An experimental engine weighing 480 lb is mounted on a test stand with spring mounts at A and B, each with a stiffness of 600 lb/in. The radius of gyration of the engine about its mass center G is 4.60 in. With the motor not running, calculate the natural frequency of vertical vibration and of rotation about G. If vertical motion is suppressed and a light rotational imbalance occurs, at what speed N should the engine not be run?