Find the Time When Rocket Uses Up Its Fuel: Graph Analysis

In summary, the conversation discusses the time at which a rocket uses up its fuel, based on a graph showing velocity over time. The experts correct the initial answer of 20 seconds and explain that the rocket actually reaches its maximum speed at 20 seconds, but it takes an additional 10 seconds for the gravitational force to decelerate it back to zero velocity. They also discuss the relationship between the rocket's maximum speed and the force of gravity.
  • #1
nicholaschean
20
0
A rocket is launched vertically upwards until it uses up its fuel. It then falls back to Earth. Find the time when the rocket uses up its fuel from the graph.
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My answer was 20s. Is it correct?
 
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  • #2
[EDIT]This information is wrong, I made a mistake.

It's rather difficult to make out what your axis are labeled as. and that is the crucial part of this problem.

It seems that your x-axis is labeled: t/s
which I would take to mean that axis is time in seconds.
and I think your y-axis is labeled: v/ms^(-1)
which I would take to mean that axis is velocity, with units of meters per second.
Be careful about that in the future because '/' means divide. Or maybe you were using '|' instead to divide the two?

Either way, if those assumptions are correct, then I think your answer is wrong.

You probably guessed 20s because that is where it appears to 'turn around' but if I am correct and that is a velocity graph, then it is a bit trickier than that. Because look at the peak again, it is still positive, not zero. So therefore your velocity is still positive meaning it is still going up.
 
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  • #3
Gear.0 said:
You probably guessed 20s because that is where it appears to 'turn around' but if I am correct and that is a velocity graph, then it is a bit trickier than that. Because look at the peak again, it is still positive, not zero. So therefore your velocity is still positive meaning it is still going up.

The direction of motion has nothing to do with the net force, which is directly related to the engine or the fuel.
Though that's not the tricky part, the problem is quite tricky: it may be easy to get the right answer, but it's not easy to get the right reason. The answer of the OP is correct, but I would like to hear an explanation from the OP :smile:
 
  • #4
Oh yes, I apologize OP I was wrong. For some reason when I was responding I thought it was asking when the rocket turns around instead of when it runs out of fuel.

disregard my post, listen to hikaru1221.
 
  • #5
I think the answer is correct. It is 20 second because the rocket will accelerate until it runs out of fuel at this point the rocket reaches his maximum speed and then the gravitational force plays its role in pulling the rocket which means decreasing the speed or decelerating from the maximum.
 
  • #6
the_storm said:
I think the answer is correct. It is 20 second because the rocket will accelerate until it runs out of fuel at this point the rocket reaches his maximum speed and then the gravitational force plays its role in pulling the rocket which means decreasing the speed or decelerating from the maximum.

If I change the value 30 (s) to 40, is the answer still 20s?
 
  • #7
No. and the maximum Velocity won't be 100 m/s.Correct?
 
  • #8
I mean, just change the graph a bit by changing the value 30 to 40, the other things remains the same.
 
  • #9
So you mean the maximum speed will be in 20 s ?
 
  • #10
Yes, the rocket reaches its max speed at t=20s.
 
  • #11
If the zero Velocity at 40s I don't thinks the maximum speed is at 20s
why ?
because at 20s after the fuel runs out, the force of the gravity takes 10s to decelerate the velocity from 100 to 0, so if the gravitational force is constant and the maximum speed is 100 why does the gravity take 20s to decelerate the velocity to 0 ? You get my point ?
 
  • #12
Now you get a bit of my point. Think about this. Is it true that the moment the rocket reaches maximum speed is the moment it uses up fuel? Is it the right reason?
 

1. How do you determine the time when a rocket will use up its fuel?

The time when a rocket uses up its fuel can be determined by analyzing its fuel consumption rate and the amount of fuel it has at the start. This can be done by plotting a graph of the rocket's fuel usage over time and finding the point where the line intersects the x-axis, which represents the time when the fuel is completely used up.

2. What factors affect the rate at which a rocket uses up its fuel?

The rate at which a rocket uses up its fuel can be affected by various factors such as the rocket's weight, the type of fuel used, and the speed at which it is traveling. Other factors include the rocket's design, atmospheric conditions, and any external forces acting on the rocket.

3. Is there a specific equation or formula for finding the time when a rocket uses up its fuel?

Yes, there is a specific equation that can be used to find the time when a rocket uses up its fuel. This equation is known as the rocket equation and it takes into account the rocket's initial mass, final mass, and specific impulse to calculate the time when the rocket will run out of fuel.

4. Can a rocket's fuel usage be predicted accurately?

While it is possible to predict a rocket's fuel usage, it is not always 100% accurate. This is because there are many variables and factors that can affect the rate at which a rocket uses up its fuel. However, with advanced technology and precise calculations, scientists can make fairly accurate predictions.

5. How does the analysis of a rocket's fuel usage help in space exploration?

The analysis of a rocket's fuel usage is crucial in space exploration as it helps in planning and executing missions effectively. By understanding the rate at which a rocket uses up its fuel, scientists can determine the maximum distance a rocket can travel, how long it can stay in orbit, and when it will need to refuel. This information is essential in ensuring the success of space missions.

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