- #1

Sarah0001

- 31

- 1

## Homework Statement

A rocket, total mass 1.00 × 10^4 kg, is launched vertically; eighty per cent of the mass being fuel. At ignition, time t = 0, the thrust equals the weight of the rocket. The ejected exhaust gases have a speed of 9.00 × 10^2 ms ^–1. Assuming the rate of fuel consumption and the acceleration due to gravity are constant,

calculate: (i) the mass, m, of gases ejected per second (ii) the acceleration, a

_{e}, of the rocket when the fuel is almost exhausted at time t

_{e}

The part I am stuck on is part ii - I am confused on how the thrust is equal to 1.00 × 10^4 * g as seen on the uploaded work solutions below.

F net = Thrust - Weight of rocket

Total Mass of rocket * net acceleration = Thrust - 0.2* total mass rocket *acceleration due to gravity

I am confused on how the Thrust is equal to the weight of the total mass of the rocket. Is there a physical explanation for this

## Homework Equations

F=ma

W = Mg

**3. My attempt at a solution**

Am I correct in my logic that since the exhaust gases cause the thrust of the rocket, then

the net acceleration of the rocket would be the mass of the exhaust gases at time t

_{e}multiplied by acceleration due to gravity and this product divided by the mass of the rocket, as this is what the thrust force is acting on.

Although this gets to the same numerical answer, I am not convinced I used Newton's Second Law in terms of the worked solutions as I am currently unable to understand how thrust at that time where fuel is nearly exhausted, equals 1.00*10^4 *g. I just thought that thrust equals the exhaust gases * g , and acting on the rocket. I feel there is something wrong in my understanding.