Determine the amplitude of vertical vibration of
the spring-mounted trailer as it travels at a velocity of 25
km/h over the road whose contour may be expressed by a
sinusoid. The mass of the trailer is 500 kg and that of the
wheels alone may be neglected. During loading, each 75 kg
added to the load caused the trailer to sag 3 mm on its
springs. Assume that the wheels are in contact with the road
at all times and neglect damping. At what critical speed vc is
the vibration of the trailer greatest? [J. L. Meriam & L. G.
Kraige 8/71]