2 1 points My No A model rocket engine has an average thrust

2. 1 points My No A model rocket engine has an average thrust of 6.7 N. It has an initial mass of 28 g, which includes fuel mass of 10.8 g. The duration of the burn is 2.91 s. (a) What is the average exhaust speed of the engine? (b) The engine is placed in a rocket body of mass 58.8 g and fired from rest in zero gravity by an astronaut in space. What is the rocket\'s final speed if fuel burns at a constant rate? O Show My Work (Optional)

Solution

a) dM / dt = 10.8 * 10^-3 / 2.91 = 3.71 * 10^-3 kg/s

thrust P = -V * dM/dt

6.7 = V * 3.71 * 10^-3

average exhaust speed = 1805 m/s

b) V_f -V_i = V * ln (M_i / M_f)

V_f = 1806 * ln [ (58.8 + 28) / (58.8 + 28 - 10.8) ]

rocket\'s final speed= 240 m/s