The grain in a solid propellant rocket is a hollow cylinder bonded to the casing so that it burns only on its inner cylindrical surface and on one end. Its density is 1650 kg/m3 , and its burning rate is characterized by r = 13.3(P0 MPa)0.63 mm/s. At a point in the burning period when P0 = 0.7 MPa, the grain d/D = 0.4 and L/D = 6, L being the grain length and d and D being its inner and outer diameters. Determine the rate of change of chamber pressure, assuming the gas temperature stays constant at 2750 K and that the gas specific heat ratio is 1.24. D = 1 m.