Hard equation (for me anyways) help

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In summary, the problem involves integration and the rocket is taken out to space with no external forces acting on it. The rocket has a total mass of 363kg, with 333kg of fuel and a weight of 30kg. The rate of fuel burn is 2.6kg/s and the engine can run for 128 seconds. The thrust force of the engine is 4990N and the acceleration initially is 13.74m/s. The total weight of the rocket is 363kg. Just before all the fuel is used up, the acceleration is 166.8m/s and the total weight is 30kg. The question asks for the maximum speed when all fuel has been used, and this can be solved
  • #1
phlik
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well atleast i think this problem involves integration. i also duno how to derive this into a formula.

ok, so this rocket is taken out to space so there are no external forces acting on it (ie if the rocket moves at 2m/s it will continue to move at that speed FOREVER as there is no other forces acting on it).

total mass of the rocket is 363kg, fuel in the rocket is 333kg. (wiehgt of actual rocket itself is 363-333=30kg). the rate at which the fuel is burnt is 2.6kg/s therefore the engine can run for 128seconds because 333/2.6=128. the thrust force of the engine is 4990N (N = Newtons). now force=acceleration x mass therefoer acceleration=force/mass.

when the rocket starts up the velocity is zero, the acceleration initially is 13.74m/s and the total weight of the rocket is 363kg. and just before all the fuel has ran out the acceleration is now 166.8m/s the total weight of the rocket is 30kg.

ok so that's all the information you can use (you don't have to use all the information). the QUESTION is "what is the maximum speed when all of the fuel has been used". obviously thoughout the whole time (128seconds) the force comming out of the engine is 4990N and as the fuel is used up, the mass decreases and therefore acceleration increases so the rate of velocity will increase because there is no other external forces on the system except for the thrust force.

ive been trying to do this question for a long time but unsuccessful. the only way i think this can be done is by integration but i have no idea how to derive this into a formula. yes it is a physics question but science i have given all information needed it can be done using maths. much help will be appreciated (as there's a few of us trying to do this same question) thanks.
 
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  • #2
Accelaration is rate of change of velocity. Since F=ma, a=F/m=dv/dt
Mass of the rocket varies with time, every second it reduces 2.6kg from 363kg
so m=363-2.6t
a=4990/m=4990/(363-2.6t)=dv/dt
dv=4990 dt/(363-2.6t)
Integrating, you get v=4990/2.6 * ln (Initial mass / final mass)
=4990/2.6*2.4932
=4785m/s
phlik said:
well atleast i think this problem involves integration. i also duno how to derive this into a formula.

ok, so this rocket is taken out to space so there are no external forces acting on it (ie if the rocket moves at 2m/s it will continue to move at that speed FOREVER as there is no other forces acting on it).

total mass of the rocket is 363kg, fuel in the rocket is 333kg. (wiehgt of actual rocket itself is 363-333=30kg). the rate at which the fuel is burnt is 2.6kg/s therefore the engine can run for 128seconds because 333/2.6=128. the thrust force of the engine is 4990N (N = Newtons). now force=acceleration x mass therefoer acceleration=force/mass.

when the rocket starts up the velocity is zero, the acceleration initially is 13.74m/s and the total weight of the rocket is 363kg. and just before all the fuel has ran out the acceleration is now 166.8m/s the total weight of the rocket is 30kg.

ok so that's all the information you can use (you don't have to use all the information). the QUESTION is "what is the maximum speed when all of the fuel has been used". obviously thoughout the whole time (128seconds) the force comming out of the engine is 4990N and as the fuel is used up, the mass decreases and therefore acceleration increases so the rate of velocity will increase because there is no other external forces on the system except for the thrust force.

ive been trying to do this question for a long time but unsuccessful. the only way i think this can be done is by integration but i have no idea how to derive this into a formula. yes it is a physics question but science i have given all information needed it can be done using maths. much help will be appreciated (as there's a few of us trying to do this same question) thanks.
 
Last edited:
  • #3
thank you very much, that helped a lot.
 

1. What is a hard equation?

An equation is considered "hard" when it involves complex mathematical concepts or requires advanced problem-solving skills to solve.

2. How do I know if an equation is hard?

An equation can be considered hard if it contains multiple variables, unknowns, or complicated functions, or if it is beyond your current skill level in mathematics.

3. How can I solve a hard equation?

Solving a hard equation requires a strong understanding of basic mathematical principles and the use of advanced problem-solving techniques such as substitution, elimination, or graphing. It may also be helpful to break the equation down into smaller, more manageable parts.

4. Can I use a calculator to solve a hard equation?

While a calculator can sometimes be helpful in solving a hard equation, it is important to have a solid understanding of the underlying math concepts and to use the calculator as a tool, rather than relying on it completely.

5. What resources can I use to help me solve a hard equation?

There are many resources available to help with solving hard equations, including textbooks, online tutorials, and math forums where you can ask for help from experts and other students. It is also important to practice regularly and seek help from a teacher or tutor if needed.

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