Accelerated Motion Problem (Rockets)

Question

Physics students are studying the motion of a bottle rocket. The bottle rocket has a weight of 20 N.

1. What force is being provided by the propulsion if the rocket is accelerating upwards at 5 m/s2 ?

2. If the propulsion force provided by the escaping liquid is 50 N, what upward acceleration will the rocket have?

3. During one trial of the bottle rocket, the students decide to lay the bottle rocket down horizontally on a surface with negligible friction. They notice that when the rocket starts, it moves with an acceleration of 30 m/s2. What must be the propulsion force in this case?

Answer 1

m = 20 / 9.81 kg

F=ma

Net force upwards = (20 / 9.81) x 5

If P = force from propulsion then P - mg = (20/9.81) x 5

P - 20 = (20/9.81) x 5

P = 20 + (20/9.81) x 5

For (2)

Net force upwards = 50 - mg

Acceleration = F/m = (50/m) - g = (50/ (20/9.81)) - 9.81

In (3) as there is negligible friction, F=ma. a = 30, m = (20/9.81), you can calculate F