Rocket Fuel Consumption: Calculation of 80kN Takeoff Rate

Click For Summary

Homework Help Overview

The discussion revolves around calculating the fuel consumption rate of a rocket at the moment of takeoff, given its weight and the velocity of the ejected combustion products. The problem is situated within the context of dynamics and rocket propulsion.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to apply the equation f = m(dv/dt) + v (dm/dt) and p = mv but reports difficulty in arriving at the correct answer. Participants inquire about the specifics of the attempts made to identify potential misunderstandings.

Discussion Status

Participants are actively engaging with the problem, with some offering hints and guidance to clarify the concepts involved. There is an exploration of the necessary acceleration for takeoff and the relationship between mass, velocity, and acceleration, indicating a productive direction in the discussion.

Contextual Notes

The original poster notes that this question is not part of coursework but rather from an old textbook, which may influence the context in which the problem is approached.

icymage
Messages
2
Reaction score
0
The weight of a rocket is 80kN at the instant it takes off , and the products of the combusion are ejected at a velocity of 0.60 kms-1 relative to the rocket. Calculate the rate at which the rocket must be consuming fuel in order to take off vertically. Ans: 134kgs-1

Cant find a solution despite numerous attempt , anyone can help ?
 
Physics news on Phys.org
Welcome to PF icymage,

Could you perhaps detail your attemps to that we can see where your going wrong?
 
hmm i tried using the equation f = m(dv/dt) + v (dm/dt) and p = mv and i can't get the answer. Anw this isn't coursework/schoolwork it is a question i stumbled upon on a old textbook of mine.
 
icymage said:
hmm i tried using the equation f = m(dv/dt) + v (dm/dt) and p = mv and i can't get the answer. Anw this isn't coursework/schoolwork it is a question i stumbled upon on a old textbook of mine.
Take a look at this excellent https://www.physicsforums.com/showthread.php?t=199087" by D_H, and see if it helps clarify things.
 
Last edited by a moderator:
Welcome to PF!

icymage said:
hmm i tried using the equation f = m(dv/dt) + v (dm/dt) and p = mv and i can't get the answer.

Hi icymage! Welcome to PF! :smile:

This isn't really a caluclus question … it would be if you were asked to find the fuel used to reach a certain time, for example … but you're only asked for the initial fuel used while the speed is zero.

Hint: how much acceleration does the fuel have to produce before the rocket lifts off?

how much mass and velocity produce that acceleration? :smile:
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
Replies
3
Views
2K
Replies
4
Views
6K
  • · Replies 2 ·
Replies
2
Views
3K
Replies
1
Views
3K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 4 ·
Replies
4
Views
7K
  • · Replies 1 ·
Replies
1
Views
3K