Calculating Speed of a Rocket Using Mass and Thrust

In summary, the conversation is about finding the speed of a rocket based on the given data of a mass of 150 grams, engine thrust of 1700 grams for 4 seconds, and the person asking for help to calculate it. The conversation also mentions the difficulty of converting engine thrust from grams to newtons and the complication of changing mass during the rocket's movement. The solution is suggested to be found through the Tsiolkovsky rocket equation.
  • #1
qalz
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Hi guys, I would like to count sth., but to do that i need a speed of thing. The promblem is that I've got mass ~150 gram (0,33 pound), enginee thrust 1700 gram (3,75 pound) which work 4 seconds (it moves up) and I don't know how to count this. Do you know, it is possible to count speed based on that data?
Sorry for the low level of English, I'm from Poland (there is no forum where somebody helped me). :/
 
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  • #2
qalz said:
engine thrust 1700 gram
Engine thrust cannot be in grams.
 
  • #3
Find the engine thrust in Newtons, subtract from it ( 0.15 * 9.81 ), leaving the net force, calculate the acceleration rate, accelerate for 4 seconds, use Newtons rules of motion for the solution ( final velocity).
 
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  • #4
Sorry, this is power of engine. I measured it putting engine upside-down on weight :)
 
  • #5
Did you zero the scales before firing the rocket? I assume you did so..

1.7kg equates to 1.7*9.81 = 16.7N of thrust.

The total force on your rocket is

16.7N - (0.15 * 9.81) = 14.4N

The acceleration is given by F=ma or a=F/m

a = 14.4/0.15 = 96m/s/s

That's very fast. I suspect if you use that figure to calculate the velocity after 4 seconds you will get a figure that is too fast. eg You can't ignore air resistance.
 
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  • #6
If this is a rocket, the problem is further complicated by the fact that the mass changes during the four-second period as the propellant is burned. Try googling for "Tsiolkovsky rocket equation"; you'll find what you need there.
 
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  • #7
Yes, that's a rocket. I'll google it, thanks for help :)
 

FAQ: Calculating Speed of a Rocket Using Mass and Thrust

How is speed obtained from thrust?

Speed is obtained from thrust through the principle of Newton's 2nd Law of Motion, which states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. In simpler terms, the more thrust (force) applied to an object, the faster it will accelerate.

What factors affect the speed obtained from thrust?

Several factors can affect the speed obtained from thrust, including the amount of thrust applied, the mass of the object, the direction of the thrust, and external forces such as air resistance or friction. The design and efficiency of the engine or propulsion system also play a significant role in determining the speed obtained from thrust.

How does the shape of an object affect the speed obtained from thrust?

The shape of an object can significantly affect the speed obtained from thrust. Objects with streamlined shapes, such as airplanes or rockets, are designed to reduce air resistance and allow for a higher speed with the same amount of thrust. On the other hand, objects with a larger surface area, such as ships, may require more thrust to achieve the same speed due to the increased drag caused by their shape.

Can thrust be used to increase speed indefinitely?

No, thrust cannot be used to increase speed indefinitely. As an object's speed increases, air resistance and other external forces also increase, making it more difficult for the object to accelerate. Eventually, the object will reach a maximum speed known as terminal velocity, where the forces acting on it are balanced, and it can no longer accelerate.

How can thrust be increased to achieve a higher speed?

Thrust can be increased by either increasing the amount of force produced by the engine or by reducing the mass of the object. This can be achieved through various methods such as using more powerful engines, optimizing the design of the engine or propulsion system, or reducing the weight of the object. However, there are limitations to how much thrust can be increased, as it also depends on other factors such as air density and atmospheric conditions.

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