2. consider a situation where change in momentum come from a change in mass rather than that coming from a change in velocity of an object: rocket propulsion. the propelling gases exert force on the rocket. the gases are expelled at a rate of r = 1300 kg/s with a speed of v = 4.5 × 104 m/s. a) what is the mass expelled in time ∆t. label this mass ∆m. b) how much momentum does the mass carry, in terms of ∆t, r, and v. c) use the relationship between the average force and change in momentum to obtain the expression for the average force in terms of r and v and calculate its value.