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A ring of radius \(R=4 \mathrm{~m}\) made of a highly dense material has a mass \(m_{1}=5.4 \times 10^{9} \mathrm{~kg}\) distributed uniformly over its circumference. A highly dense particle of mass \(m_{2}=6 \times 10^{8} \mathrm{~kg}\) is placed on the axis of the ring at a distance \(3 \mathrm{~m}\) from the center of the ring. Find the speed of the particle (in \(\mathrm{cm} / \mathrm{s}\) ), when the particle is at the center of the ring. Except mutual gravitational interaction of the two, neglect all other forces.

Short Answer

Expert verified
The particle will have a speed of approximately 1320 cm/s at the center of the ring.

Step by step solution

01

Understand the Problem Context

This problem involves a ring and a particle with given masses and positions. We need to find the speed of the particle as it moves under the influence of gravitational force towards the center of the ring, without any other forces in play.
02

Determine Potential Energy at Initial Position

The initial potential energy when the particle is on the axis of the ring, 3 meters from its center, is given by the gravitational potential energy formula: \[ U = -G \frac{m_1 m_2}{ ext{Distance}} \] Compute Distance as \( \sqrt{R^2 + 3^2} = \sqrt{4^2 + 3^2} \), \[ U = -G \frac{5.4 \times 10^9 \times 6 \times 10^8}{5} \].
03

Determine Potential Energy at the Center

When the particle reaches the center, the potential energy is calculated by minimizing the distance (which is the radius) \[ U = -G \frac{m_1 m_2}{R} \] \[ U = -G \frac{5.4 \times 10^9 \times 6 \times 10^8}{4} \]
04

Use Conservation of Energy

The difference in potential energy as the particle moves from its initial position to the center converts to kinetic energy \[ \Delta U = -\left(-G \frac{5.4 \times 10^9 \times 6 \times 10^8}{4} + G \frac{5.4 \times 10^9 \times 6 \times 10^8}{5} \right) \] \[ \Delta U = \frac{1}{2} m_2 v^2 \], solve for \( v \).
05

Solve for Velocity

Substitute known values and solve \[ \frac{1}{2} \times 6 \times 10^8 \times v^2 = -G \times 5.4 \times 6 \times 10^{17} \left(\frac{1}{4} - \frac{1}{5}\right) \] \[ v = \sqrt{\frac{2G \times 1.08 \times 10^{17}}{6 \times 10^8}} \]. Converting \( v \) to cm/s involves multiplying by 100.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Conservation of Energy
In physics, the conservation of energy principle tells us that energy cannot be created or destroyed; it can only be transformed from one form to another. This principle is crucial in solving problems involving gravitational potential and kinetic energy. In the context of the given exercise, conservation of energy helps us understand how the potential energy, due to the gravitational field created by the ring and particle, is converted into kinetic energy. When the particle initially is 3 meters away from the ring's center, it possesses a certain amount of gravitational potential energy. As it moves towards the ring's center, this potential energy is transformed into kinetic energy, increasing the speed of the particle.

For this problem, we calculate the difference in potential energy as the particle moves from its initial position to the center of the ring. This difference in energy manifests as kinetic energy of the moving particle. By equating the loss in potential energy to the gain in kinetic energy, we can solve for the particle's speed when it reaches the ring’s center.
Kinetic Energy
Kinetic energy is the energy that an object possesses due to its motion. Mathematically, it is given by \[{\text{Kinetic Energy} = \frac{1}{2}mv^2}\] where \(m\) is the mass of the object and \(v\) is its velocity. In this exercise, the particle starts at rest with no initial kinetic energy but gains kinetic energy as it moves closer to the center of the ring due to the gravitational attraction. We'll find that as the potential energy decreases, the kinetic energy increases, given the conservation of energy principle.

Our goal is to find the speed of the particle, \(v\), when it is at the center of the ring using the change in potential energy. The kinetic energy gained by the particle is equal to the loss in gravitational potential energy, allowing us to solve for the velocity.
  • The mass \(m\) of the particle is \(6 \times 10^8 \text{ kg}\).
  • The change in gravitational potential energy is converted into kinetic energy.
Substituting the values and solving the equation gives us the speed of the particle at the center.
Gravitational Force
Gravitational force is a universal force that attracts two bodies towards each other. It depends on the masses involved and the distance between them. In our exercise, the gravitational force acts between a highly dense ring and a particle. This force is responsible for pulling the particle towards the center of the ring. The formula for gravitational force between two masses is given by:

\[{F = G \frac{m_1 m_2}{r^2}}\]
where \(G\) is the gravitational constant, \(m_1\) and \(m_2\) are the masses, and \(r\) is the distance between the centers of the two objects. In this problem, as the particle approaches the center of the ring, the effective distance changes, influencing the amount of force exerted.

The gravitational force also dictates how the particle's potential energy changes as it moves. Initially positioned away from the ring, we calculate the potential energy and gravitational force accordingly. As the particle moves, these values adjust seamlessly into kinetic energy through the conservation of energy, emphasizing the interlinked relationship of gravitational force with energy transformations in this scenario.

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