# Finding Maximum Momentum of a Rocket in Vacuum

• LANS
In summary, the problem involves finding the maximum value of momentum for a rocket with decreasing mass and increasing speed. The Tsiolkovsky rocket equation is used to define momentum in terms of current mass, and the derivative is taken to find the maximum value of p(m). However, there appears to be a mistake in the derivative calculation.
LANS

## Homework Statement

A rocket of initial mass $$m_{0}$$ accelerates from rest in vacuum in the absence of gravity. As it uses up fuel, its mass decreases but its speed increases. For what value of $$m$$ is its momentum $$p = mv$$ maximum?

## Homework Equations

Tsiolkovsky rocket equation:

$$v(m) = v_e ln \left( \frac{m_0}{m} \right)$$

## The Attempt at a Solution

multiply both sides of rocket equation by m to get momentum in terms of current mass.

$$mv = v_e ln \left( \frac{m_0}{m} \right) *m$$
$$p(m) = v_e ln \left( \frac{m_0}{m} \right) *m$$

Find the maximum p(m) by differentiating and letting $$\frac{dp}{dt} = 0$$

$$\frac{dp}{dt} = v_e \left( \frac{m_0}{m} \right) + v_e ln \left( \frac{m_0}{m} \right)$$

$$0 = v_e \left( \frac{m_0}{m} \right) + v_e ln \left( \frac{m_0}{m} \right)$$

moving the ln term to the other side

$$-v_e ln \left( \frac{m_0}{m} \right) = v_e \left( \frac{m_0}{m} \right)$$
$$v_e ln \left( \frac{m}{m_0} \right) = v_e \left( \frac{m_0}{m} \right)$$

$$v_e$$ cancels out.

$$ln \left( \frac{m}{m_0} \right) = \left( \frac{m_0}{m} \right)$$

Here's where I get stuck. I can't seem to define m in terms of m_0. Any suggestions? Am I approaching the problem wrong?

Any help is appreciated.

Thanks.

Last edited:
LANS said:
$$\frac{dp}{dt} = v_e \left( \frac{m_0}{m} \right) + v_e ln \left( \frac{m_0}{m} \right)$$
Looks like you made a mistake in taking the derivative - the right side of this isn't correct. (Also note that what you're calculating here is not dp/dt, since the variable you're taking the derivative with respect to is not t.)

## What is the maximum momentum of a rocket in a vacuum?

The maximum momentum of a rocket in a vacuum is determined by its mass and velocity, according to the formula p = mv, where p is momentum, m is mass, and v is velocity. This means that the heavier and faster the rocket is, the greater its maximum momentum will be.

## How does air resistance affect the maximum momentum of a rocket in a vacuum?

In a vacuum, there is no air resistance, so it does not affect the maximum momentum of a rocket. This is why rockets are typically launched in a vacuum or in outer space where there is no air resistance to slow them down.

## What factors can impact the maximum momentum of a rocket in a vacuum?

The maximum momentum of a rocket in a vacuum can be impacted by its mass, velocity, and any external forces acting upon it. Other factors such as the design and efficiency of the rocket's engines can also affect its momentum.

## How is the maximum momentum of a rocket in a vacuum calculated?

The maximum momentum of a rocket in a vacuum is calculated using the formula p = mv, where p is momentum, m is mass, and v is velocity. This formula applies to all objects in motion, including rockets.

## Why is it important to calculate the maximum momentum of a rocket in a vacuum?

Calculating the maximum momentum of a rocket in a vacuum is important for understanding its capabilities and limitations. This information is crucial for designing and launching successful space missions, as well as ensuring the safety of astronauts and equipment on board the rocket.

### Similar threads

• Special and General Relativity
Replies
3
Views
3K
• Advanced Physics Homework Help
Replies
7
Views
3K
• Mechanics
Replies
4
Views
2K
• Advanced Physics Homework Help
Replies
2
Views
2K
• Introductory Physics Homework Help
Replies
2
Views
1K
• Introductory Physics Homework Help
Replies
12
Views
955
• Introductory Physics Homework Help
Replies
4
Views
1K
• Introductory Physics Homework Help
Replies
13
Views
1K
• Advanced Physics Homework Help
Replies
7
Views
1K
• Advanced Physics Homework Help
Replies
10
Views
2K