Rocket Mass & Velocity: Calculating Gas Ejection Rate

  • Thread starter Thread starter hjr
  • Start date Start date
  • Tags Tags
    Mass
Click For Summary

Homework Help Overview

The problem involves calculating the gas ejection rate for a rocket traveling at a specific velocity and altitude, aiming to achieve a desired acceleration. The context includes concepts from dynamics and rocket propulsion.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster attempts to solve for the gas ejection rate using a given equation but expresses uncertainty about identifying all external forces involved. Some participants question the assumption that gravitational force is simply mg at the specified altitude.

Discussion Status

Participants are exploring the nature of the external forces acting on the rocket, with some guidance provided regarding the calculation of gravitational force at altitude. There is an acknowledgment of the need to consider the distance from the center of the Earth in these calculations.

Contextual Notes

There is a focus on the gravitational force's dependence on altitude, and the original poster is seeking clarification on how to accurately account for this in their calculations.

hjr
Messages
8
Reaction score
0

Homework Statement


A rocket traveling 1950 m/s away from the Earth at an altitude of 6600 km fires its rockets, which eject gas at a speed of 1300 m/s (relative to the rocket).
If the mass of the rocket at this moment is 2.25×104 kg and an acceleration of 1.4 m/s^2 is desired, at what rate must the gases be ejected?

Homework Equations



M*dv/dt = \sum F(ext) + v(rel)*dM/dt

The Attempt at a Solution



I thought i could just solve for dM/dt in the above equation and plug in the numbers to get the answer but that didnt work. I think my problem is with finding all the external forces, which i think is just mg. I just need a hint to start.
 
Physics news on Phys.org
*bump*
 
The external force at altitude of 6600 km is not mg.

ehild
 
ehild said:
The external force at altitude of 6600 km is not mg.

ehild

so when I find g is that all i have to find? ->for the external force?
 
Last edited:
The external force is gravity that depends on the altitude.
F=GmM/r2, and r is the distance from the centre of Earth, r=radius or Earth + altitude

ehild
 
alright thanks
 

Similar threads

How Does Rocket Ejection Mass Affect Its Velocity in Space?
  • · Replies 1 ·
Replies
1
Views
2K
Rocket ejecting mass in a direction perpendicular to its velocity
  • · Replies 6 ·
Replies
6
Views
1K
Rocket acceleration problem: confused about Newton's 2nd Law
  • · Replies 42 ·
2
Replies
42
Views
6K
Rocket + Connected Body Dynamics problem
  • · Replies 47 ·
2
Replies
47
Views
3K
Trouble with a Rocket Propulsion question (Variable Mass & Momentum)
  • · Replies 2 ·
Replies
2
Views
2K
How Does the Relativistic Rocket Equation Describe Velocity?
  • · Replies 2 ·
Replies
2
Views
2K
How to calculate velocity of infinite-stage rocket?
  • · Replies 2 ·
Replies
2
Views
1K
Rocket Launch: Achieving Escape Velocity w/ Fuel-Mass Ratio of 300
  • · Replies 3 ·
Replies
3
Views
2K
How Fast Will the Rocket Travel After Using All Its Fuel?
  • · Replies 7 ·
Replies
7
Views
2K
How Is Rocket Speed and Height Calculated Under Varying Thrust and Mass?
  • · Replies 13 ·
Replies
13
Views
2K