[填空题]
A block of jello rests on a plate as shown in Fig. 11–ha:s jr ; i.8,cppju8e58 (which also gi)peu6 sg. 4klxves the dimensions of the block). You push it sideways as shown, and then you let go. The jello springs back and begins tokpx) ue4 gs.l6 vibrate. In analogy to a mass vibrating on a spring, estimate the frequency of this vibration, given that the shear modulus (Section 9–5) of jello is 520 $N/m^2$ and its density is 1300 $kg/m^3$ Hz