The velocity of longitudinal sound waves in liquid helium 4he, at temperatures below 0.6 k, is v = 238.3 m/s. within the liquid there are no transverse displacement waves. the density is rho = 145 kg/m^3. using the data above, determine the debye temperature in liquid helium in k. note that the number of modes describing displacements in one direction should be equal to n, rather than 3n. calculate the low-temperature heat capacity for helium, per mass, within the debye theory, and compare to the experimental result of cv/m = 20.4 t^3, where t is in k and c v/m is in j/(kg. k).