Using (10.22) and (12.13) find an expression for the gravitational potential energy density (per unit volume), u. in a molecular cloud core that depends on (only) the core mass and initial density. b) Estimate u, for the molecular core described in Problem #1, using the Jeans mass for the core mass. Use equation (1 1.9) to estimate the magnetic energy density, up, if the cloud has an initial (uniform) field strength of B = 4 nT. Compare this value to part (a). Is the magnetic field important at this stage of star formation? Note that un in (1 1.9) is the permeability constant, not the mean molecular mass