A small trailer and its load have a total weight of 500-lb. The trailer is supported by two springs, each of constant 350 lb ft, and is pulled over a road, the surface of which can be approximated by a sine curve with an amplitude of 2 in. and a wavelength of 15 ft (that is, the distance between successive crests is 15 ft and the vertical distance from crest to trough is in) Determine (a) the speed atl which resonance will occur, (b) the amplitude of the vihration of the trailer at a speed of 30 mi h.