Is the Rocket Equation True?

I want to help you. But I don't have the time to read all the previous posts and try to figure out what you are trying to solve. Please do post a proper problem statement. In summary, the conversation discusses an equation and its validity in relation to finding the net force of a rocket. The equation states that net force is equal to the mass times the change in velocity all over time. However, it is mentioned that this formula is not valid for a thrusting rocket and the Tsiolokovsky rocket equation should be used instead. The conversation also includes details about finding the velocity and height of the rocket.
  • #1
cashman91
8
0
is this equation true

Fnet=[m(Vf-Vi)]/Delta T

net force is equal to the mass times the change in velocity all over time

thanks alot
 
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  • #2
cashman91 said:
is this equation true

Fnet=[m(Vf-Vi)]/Delta T

net force is equal to the mass times the change in velocity all over time

thanks alot

Well if it was reexpressed as

[tex] F_n_e_t=m(\frac{v_f-v_i}{\Delta t}) [/tex]

Does that help?
 
  • #3
It should be the average force over time delta t in place of Fnet.
 
  • #4
the formula malty gave is correct but how can you verify this formula is correct

I get where shooting star is coming from but i need to find the net force of the rocket

so far all i know is my two inclinometer reader posted scores of 53 and 54 degrees with a time of 1.03/1.07 seconds the mass of the rocket and the mass of an empty and full engine

i can solve the net force but i need to verfiy the formula is correct or not

this formula came out of a Nelson physics 11 book i don't have access to the answer manual if i did it would tell me if this formula is correct or not
 
  • #5
malty and I have given the same formula.

Does the book define what is net force? Why don't you tell us what is meant by that? It's also a good idea to state the problem completely and show what you've done so far.
 
  • #6
See attached jpeg for my attepmt

I need to find the

F(thrust)
F(net)
Acceleration
Fg
Vmax

I can find Eg and Ek easily myself but the problem is with the rest
 

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  • #7
Vf would be zero becasue the rocket is at the top of it height

soooo... would Vi be 65.0m/s
If Vi is 65.0 m/s then using your formula

Fnet would equal 8372.878 Newtons**

** the (mass of the rocket full with engine)+(mass of the rocket empty)/2** is the mass of the rocket assuming the reaction is constant

am i correct?
 
  • #8
The equation [itex]\bar F = m(v_f-v_i)/\Delta t[/itex] is a direct consequence of Newton's second law and the mean value theorem for an object with constant mass. That equation is not valid for a thrusting rocket since the mass of a rocket. You need to use the Tsiolokovsky rocket equation, [itex]\Delta v = v_e\ln(m_{init}/m_{final})[/itex]. For more details, see https://www.physicsforums.com/showthread.php?t=199087".
 
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  • #9
Tsiolokovsky rocket equation i have the intial mass(beofre lauch) and final mass(after launch)

we timed how long the reaction(white smoke) took before the rocket flew so how could i findout the Ve of my rocket

thanks inadvance
cashman91
 
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  • #10
Now perhaps you understand why I'd asked you to state the problem completely. There was no indication in your first post that mass was changing. Let's wait for the attacment to get approved.
 
  • #11
figured out my Vav is 31.71 m/s
height is 68.82m and time is 2.17s

Vav=(delta d)/(delta t)
 
  • #12
still nedd help
 
  • #13
anything
 
  • #14
If you post the problem framing it properly in a single post, then people would be more inclined to help you. Maybe the whole thing is there, but nobody has the patience to gather up the pieces and fit them to find out the original problem.

I'm trying to help you.
 

1. What is the rocket equation?

The rocket equation, also known as the Tsiolkovsky rocket equation, is a mathematical formula that describes the motion of a rocket in terms of its mass, thrust, and velocity. It is used to calculate the amount of propellant needed for a rocket to reach a certain velocity, as well as the velocity that a rocket can achieve with a given amount of propellant.

2. How is the rocket equation derived?

The rocket equation was derived by Russian scientist Konstantin Tsiolkovsky in the late 19th century. It is based on Newton's laws of motion and the principle of conservation of momentum.

3. What are the assumptions made in the rocket equation?

The rocket equation makes several assumptions, including that the rocket is traveling in a vacuum, there is no external force acting on the rocket, and the mass of the rocket remains constant throughout the flight. It also assumes that the propellant is being ejected at a constant rate and velocity.

4. How accurate is the rocket equation?

The rocket equation is a simplified model and does not account for factors such as atmospheric drag and the changing mass of the rocket as propellant is used. It is most accurate for short, one-stage rocket flights. For more complex missions, more precise equations and simulations are used.

5. How is the rocket equation verified?

The rocket equation has been extensively verified through experimental data and real-world applications. It has been used to successfully launch and navigate many space missions, including the Apollo moon landings and the Mars rover missions. Additionally, engineers and scientists constantly use the equation to design and plan future rocket launches and space missions.

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