With what speed will the rocket move if the average speed of exhaust gases

With what speed will the rocket move if the average speed of exhaust gases is 1 km / h and the mass of fuel is 80% of the total mass of the rocket?

Task data: V1 (average speed of exhaust gases) = 1 km / h; m1 (fuel mass) = 0.8m.

The speed at which the rocket under consideration will move can be expressed from the equality (the law of conservation of momentum): 0.8m * V1 = 0.2m * V2, whence V2 = 0.8m * V1 / 0.2m = 0.8 * V1 / 0 , 2.

Let’s calculate: V2 = 0.8 * 1 / 0.2 = 4 km / h.

Answer: The rocket in question must move at a speed of 4 km / h.