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A proton (rest mass \(1.67 \times 10^{-27} \mathrm{~kg}\) ) has total energy that is 4.00 times its rest energy. What are (a) the kinetic energy of the proton; (b) the magnitude of the momentum of the proton; and (c) the speed of the proton?

Short Answer

Expert verified
(a) 4.50 x 10^-10 J; (b) 7.50 x 10^-19 kg·m/s; (c) 0.968c

Step by step solution

01

Understanding Total and Rest Energy

The total energy of a particle is given by \( E = 4 \times E_0 \), where \( E_0 = m_0 c^2 \) is the rest energy. For a proton, this is \( E_0 = 1.67 \times 10^{-27} \text{ kg} \times (3.00 \times 10^8 \text{ m/s})^2 = 1.50 \times 10^{-10} \text{ J} \). Therefore, the total energy \( E = 4 \times 1.50 \times 10^{-10} = 6.00 \times 10^{-10} \text{ J} \).
02

Calculate the Kinetic Energy

The kinetic energy is given by the difference between the total energy and the rest energy: \( K = E - E_0 = 6.00 \times 10^{-10} \text{ J} - 1.50 \times 10^{-10} \text{ J} = 4.50 \times 10^{-10} \text{ J} \).
03

Calculate Momentum Using Energy-Momentum Relation

The energy-momentum relation is given by \( E^2 = (pc)^2 + (m_0 c^2)^2 \). Solving for momentum \( p \): \( (6.00 \times 10^{-10} \, ext{J})^2 = (pc)^2 + (1.50 \times 10^{-10} \, ext{J})^2 \). Simplifying and solving, \( (pc)^2 = 3.375 \times 10^{-19} \text{ J}^2 \), thus \( p = \frac{\sqrt{3.375 \times 10^{-19} \, ext{J}^2}}{3.00 \times 10^8 \, ext{m/s}} = 7.50 \times 10^{-19} \text{ kg} \, ext{m/s} \).
04

Calculate the Speed of the Proton

Using \( E = \gamma m_0 c^2 \) with \( \gamma = \frac{1}{\sqrt{1-v^2/c^2}} = 4 \), solve for the speed \( v \). Reorganizing gives \( \frac{1}{4} = \sqrt{1-v^2/c^2} \). Squaring both sides gives \( \frac{1}{16} = 1 - \frac{v^2}{c^2} \). Solving for \( v \), \( \frac{v^2}{c^2} = 1 - \frac{1}{16} = \frac{15}{16} \), thus \( v = c \sqrt{\frac{15}{16}} = 0.968c \).

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Key Concepts

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

Proton
Protons are subatomic particles found in the nucleus of an atom. They have a positive electrical charge and play a crucial role in the atomic structure. Each proton carries a fundamental charge of approximately \(+1.602 \times 10^{-19}\) coulombs. They are made up of quarks and held together by the strong nuclear force, which is among the fundamental forces in nature.
A proton's rest mass is around \(1.67 \times 10^{-27} \text{ kg}\), which is used to calculate its rest energy in relativistic physics. This tiny mass is vital in computations involving high-speed particles, such as those found in accelerators or cosmic rays. Understanding the properties of protons helps in studying basic physical laws and particles' interactions.
Total Energy
Total energy in relativistic physics comprises a particle's kinetic and rest energy. This concept becomes highly significant when dealing with particles that move at speeds comparable to the speed of light. The formula used for calculating the total energy \(E\) of a particle is:
  • \(E = \gamma m_0 c^2 \)
where \( m_0 \) represents the rest mass, \(c\) the speed of light, and \( \gamma = \frac{1}{\sqrt{1-v^2/c^2}}\) is the Lorentz factor.
In the problem, the total energy is given as four times the rest energy, reflecting higher kinetic contributions. When a particle's velocity reaches a considerable fraction of the speed of light, its total energy increases significantly, surpassing the rest energy by far. This concept is essential for understanding the energetic behavior of particles in high-energy physics and cosmology.
Kinetic Energy
Kinetic energy is the energy a particle possesses because of its motion. In the realm of relativistic physics, kinetic energy calculation differs from classical physics, especially at speeds close to light speed. The kinetic energy \(K\) is calculated by subtracting the rest energy \(E_0\) from the total energy \(E\):
  • \(K = E - E_0\)
Here, the kinetic energy is substantial because the proton's total energy is much higher than its rest energy. In a real-world scenario, such a high kinetic energy could be observed in particles accelerated in particle accelerators. Understanding and calculating kinetic energy is critical in fields like astrophysics and particle physics, where high speeds and energies are prevalent.
Momentum
Momentum in relativistic contexts is more complex than the classical notion. In relativistic physics, momentum takes into account both mass and velocity, heavily affected by the Lorentz factor \(\gamma\). The equation connecting energy and momentum is:
  • \(E^2 = (pc)^2 + (m_0c^2)^2 \)
where \(p\) is momentum and \(c\) is the speed of light.
The proton's relativistic momentum is calculated using its total energy and rest mass. The momentum value obtained for high-speed particles is crucial for predicting their behavior during collisions or interactions. Accurate calculation of relativistic momentum helps physicists create models to describe phenomena in particle accelerators effectively.
Speed of Light
The speed of light, denoted by \(c\), is approximately \(3.00 \times 10^8 \text{ m/s}\). It is a fundamental constant and plays a pivotal role in the equations of relativity. In relativistic equations, it acts as a limit that cannot be surpassed by objects with mass.
When computing the velocity of a high-energy proton, we encounter Lorentz transformations. These transformations make sure that as a particle's speed approaches the speed of light, its energy becomes infinite, preventing it from reaching or exceeding \(c\). The problem illustrates how, under relativistic circumstances, the proton achieves a velocity of about \(0.968c\), showing how closely it can approach light speed without ever surpassing it. This concept is essential in understanding the ultimate speed constraints of the universe, as formulated by Einstein's theory of relativity.

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Most popular questions from this chapter

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