# What Is the Required Thrust Force to Launch a 590 kg Rocket?

• PhysicsStudent1
In summary, to accelerate a 590 kg rocket uniformly to an upward speed of 28 m/s in 3.3 s, a thrust force of 10,788 N is needed. This thrust force is produced by the rocket motor, which propels the rocket upward from the earth by expelling hot gases. The normal force and gravitational force also act on the rocket, but they cancel each other out and do not contribute to the upward acceleration.
PhysicsStudent1

## Homework Statement

A 590 kg rocket is at rest on the launch pad. What upward thrust force is needed to accelerate the rocket uniformly to an upward speed of 28 m/s in 3.3 s?

V = Vi + at
F = ma

## The Attempt at a Solution

I'm just confused about what "thrust force" actually means. Is this the same as normal force? When I solve for a using the first equation, a = 8.485.
Using the next equation, I get that F = 5006 N. Is this the upward force? Or do I need to solve for gravitational force (F=mg=5782) and then add 5006 to 5782 and get a total of 10,788 N?

If you could please clarify this for me that would be great! Thanks!

PhysicsStudent1 said:

## Homework Statement

A 590 kg rocket is at rest on the launch pad. What upward thrust force is needed to accelerate the rocket uniformly to an upward speed of 28 m/s in 3.3 s?

V = Vi + at
F = ma

## The Attempt at a Solution

I'm just confused about what "thrust force" actually means. Is this the same as normal force? When I solve for a using the first equation, a = 8.485.
Using the next equation, I get that F = 5006 N. Is this the upward force? Or do I need to solve for gravitational force (F=mg=5782) and then add 5006 to 5782 and get a total of 10,788 N?

If you could please clarify this for me that would be great! Thanks!
Draw a free body diagram of the rocket. Be careful to determine the directions in which the various forces acting on the rocket are pointing.

Thrust force is produced by the rocket motor. It's what propels the rocket upward from the earth.

PhysicsStudent1 said:
I'm just confused about what "thrust force" actually means. Is this the same as normal force?

As the rocket sits on the launch pad there is a normal force, which acts upward. The thrust force also acts upward. In both cases they are forces exerted on the rocket. The difference is that the normal force is exerted on the rocket by the launch pad whereas the thrust force is exerted on the rocket by the exhaust gases.

When I solve for a using the first equation, a = 8.485. Using the next equation, I get that F = 5006 N.

Mass times acceleration always gives you the net force.

SteamKing said:
Draw a free body diagram of the rocket. Be careful to determine the directions in which the various forces acting on the rocket are pointing.

Thrust force is produced by the rocket motor. It's what propels the rocket upward from the earth.

So I drew the FBD of the rocket and I have one arrow going upward for the normal force and one arrow going downward for the gravitational force. I haven't learned any other forces besides frictional force, so I am still not quite understanding exactly what you mean by the rocket motor producing the thrust force.

Mister T said:
Mass times acceleration always gives you the net force.

Is net force the same as normal force - gravitational force? How do I just get the thrust force?

And I apologize if I am mixing up the names of the different forces (especially normal and thrust). I thought they were the same thing

PhysicsStudent1 said:
So I drew the FBD of the rocket and I have one arrow going upward for the normal force and one arrow going downward for the gravitational force. I haven't learned any other forces besides frictional force, so I am still not quite understanding exactly what you mean by the rocket motor producing the thrust force.

Well, the act of expelling the hot gasses out of the rocket motor creates a reaction in the rocket, which propels it in the opposite direction. How do you think space rockets lift off from the launching pad?
Is net force the same as normal force - gravitational force? How do I just get the thrust force?

And I apologize if I am mixing up the names of the different forces (especially normal and thrust). I thought they were the same thing

Normal force exists only for something sitting on the ground. It's a reaction to the gravitational force trying to pull a body to the center of the earth. When something is no longer sitting on the ground, what is the normal force then?

The net force is the vector sum of all the forces acting on the rocket.

SteamKing said:
How do you think space rockets lift off from the launching pad?
When something is no longer sitting on the ground, what is the normal force then?
The thrust force? But my question is how do i calculate that? I have only learned formulas for frictional, gravitational, and normal force. I don't understand "thrust" force. Can't I just use F=ma? If not, what do I do?

SteamKing said:
Normal force exists only for something sitting on the ground. It's a reaction to the gravitational force trying to pull a body to the center of the earth.

The reaction to the normal force exerted on the rocket by the ground is the force exerted on the ground by the rocket.

The reaction to planet Earth pulling down on the rocket is the rocket pulling up on planet Earth.

PhysicsStudent1 said:
The thrust force? But my question is how do i calculate that?

You calculated that the gravitational force is 5782 N. And you calculated that the net force is 5006 N.

So, if you have a downward force of 5782 N, how much upward force do you need to get a net force (vector sum of forces) equal to 5006 N directed upwards?

Mister T said:
You calculated that the gravitational force is 5782 N. And you calculated that the net force is 5006 N.

So, if you have a downward force of 5782 N, how much upward force do you need to get a net force (vector sum of forces) equal to 5006 N directed upwards?

(I'm using negative to indicate the downward direction and x=upward force)
-5782 + x = 5006
x = 10,788 N

Is this the final answer? (and also thank you for taking the time to explain to me what net/thrust/normal force all mean)

Nice! And you're welcome. (By the way, I didn't go back and check all your work. You've got the physics right, so as long as you did the arithmetic right, you've got it.)

PhysicsStudent1

## 1. What is rocket upward thrust force?

Rocket upward thrust force is the force that a rocket engine produces to push the rocket in the opposite direction of the force, propelling it upwards. This force is created by the combustion of propellant in the rocket engine.

## 2. How is rocket upward thrust force measured?

Rocket upward thrust force is measured in Newtons (N) or pounds (lbs) and is calculated by multiplying the mass flow rate of the propellant by the velocity of the exhaust gases.

## 3. What factors affect rocket upward thrust force?

The amount of propellant, the combustion efficiency of the engine, and the velocity of the exhaust gases are all factors that can affect the rocket upward thrust force. Other factors such as the shape and design of the rocket can also impact the thrust force.

## 4. How does rocket upward thrust force affect the rocket's flight?

Rocket upward thrust force is essential for the rocket to achieve liftoff and continue its flight into space. As the thrust force increases, the rocket's acceleration also increases, allowing it to overcome the pull of gravity and move upwards at a faster rate.

## 5. Can rocket upward thrust force be controlled?

Yes, rocket upward thrust force can be controlled by adjusting the amount of propellant being burned and the shape of the nozzle. By changing these variables, the thrust force can be increased, decreased, or even turned off completely.

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