How do you calculate the enrgy required to maintain a given thrust?

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In summary, the conversation discusses the calculation of energy use per second for a hovering rocket of given mass, with the use of Thrust = Force times velocity equation. It is mentioned that the energy consumption would depend on the m(dot).a configuration, and the efficiency of the energy source. The conversation also brings up the idea of a craft powered by a jet of water, with a continuous supply of water and power. The equation W=dKE+dPE is suggested for calculating work done by non-conservative forces, and a video example is mentioned. The conversation ends with a link to a website featuring a water-powered jet pack.
  • #1
kitna paisa
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Homework Statement


I would like to be able to calculate the energy use per second, to maintain a rocket of given mass, at zero velocity, i.e. hovering, at, say, sea level.


Homework Equations


I have Thrust = Force times velocity, but can't work out the energy due to the velocity of the rocket equaling zero, leading to zero work, and apparently zero energy, whilst obviously there is considerable use of energy, and thus power.


The Attempt at a Solution

 
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  • #2
You would need to know more details about the engine to figure it out.
 
  • #3
Thanks. What I intended was to make a craft like a rocket, but which could hover. The motor could be any power plant, capable of powering a jet of water.
The water would be supplied to the craft on a continuous basis, so the craft would remain at constant mass. The power would also be provided to the craft on a continuous basis, and would most likely be electrical.
How would I work out what the energy consumption would be be in kW.Hrs for any given mass, at (craft) zero velocity, with en energy-efficiency of x%? I suspect that the result would depend on the m(dot).a configuration.
Thanks. kitna
 
  • #4
There are two forces acting on the rocket , by engine and by gravity.
The energy given by gravity is potential energy.

So W=dKE+dPE.

If you calculate work done by non conservative forces which does not include gravity then you must include the PE term.
 
  • #5
Thanks I can imagine the forces involved- no problem there. To get to the question though, what is the energy equation? There is a fine example of what I am talking about in this video. It shows just such a craft as envisaged, producing thrust to raise a mass, but how was the energy calculation made?
see http://www.break.com/index/amazing-new-water-powered-jet-pack.html
Cheers
kitna
 
  • #6
OK, the link that I gave in the previous post wasn't very good, so here is the original link for this crazy vehicle: http://jetlev.com/ !
 
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FAQ: How do you calculate the enrgy required to maintain a given thrust?

1. How is thrust related to energy?

Thrust and energy are not directly related. Thrust is a measure of force, while energy is a measure of work. However, energy is required to maintain a given thrust as it is needed to continually power the engine or device producing the thrust.

2. What factors determine the energy required for a given thrust?

The energy required for a given thrust is determined by several factors including the mass of the object being propelled, the speed at which the thrust is applied, and the efficiency of the engine or device producing the thrust.

3. How do you calculate the energy required for a given thrust?

The formula for calculating the energy required for a given thrust is: energy = force x distance. This means that the energy required is equal to the amount of force applied multiplied by the distance traveled. In the case of thrust, the distance traveled would be the distance the object is propelled forward.

4. Does the type of fuel used affect the energy required for a given thrust?

Yes, the type of fuel used can greatly affect the energy required for a given thrust. Some fuels are more efficient and produce more energy per unit, while others may be less efficient and require more energy to produce the same amount of thrust.

5. How can we reduce the energy required to maintain a given thrust?

There are several ways to reduce the energy required for a given thrust. One way is to increase the efficiency of the engine or device producing the thrust. Another way is to reduce the mass of the object being propelled, as less energy is required to move a lighter object. Additionally, optimizing the speed at which the thrust is applied can also help reduce the energy required.

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