Chapter 29: Problem 56
If a neutron moves with a speed of \(0.99 \mathrm{c},\) what are its (a) total energy, (b) rest energy, and (c) kinetic energy?
Short Answer
Expert verified
a) Total energy: \(1.06 \times 10^{-9}\) J; b) Rest energy: \(1.51 \times 10^{-10}\) J; c) Kinetic energy: \(9.08 \times 10^{-10}\) J.
Step by step solution
01
Identify the problem
We need to calculate the total energy, rest energy, and kinetic energy of a neutron moving at a speed of \(0.99c\). The rest mass of a neutron \(m\) is approximately \(1.675 \times 10^{-27} \text{ kg}\). Additionally, we will use the speed of light \(c = 3 \times 10^8 \text{ m/s.}\) For calculations, remember the formulas: total energy \(E = \gamma mc^2\), rest energy \(E_0 = mc^2\), and kinetic energy \(K = E - E_0.\)
02
Calculate the Lorentz factor (\(\gamma\))
The Lorentz factor \(\gamma\) is calculated using the formula: \[ \gamma = \frac{1}{\sqrt{1 - \frac{v^2}{c^2}}} \]Substitute \(v = 0.99c\):\[ \gamma = \frac{1}{\sqrt{1 - (0.99)^2}} = \frac{1}{\sqrt{1 - 0.9801}} = \frac{1}{\sqrt{0.0199}} \approx 7.09 \]
03
Calculate the total energy (\(E\))
Using the Lorentz factor \(\gamma\), the total energy \(E\) is given by:\[ E = \gamma mc^2 \]Substitute \(\gamma \approx 7.09\), \(m = 1.675 \times 10^{-27} \text{ kg}\), and \(c = 3 \times 10^8 \text{ m/s}\):\[ E \approx 7.09 \times 1.675 \times 10^{-27} \times (3 \times 10^8)^2 \approx 1.06 \times 10^{-9} \text{ Joules} \]
04
Calculate the rest energy (\(E_0\))
The rest energy \(E_0\) is calculated using the formula:\[ E_0 = mc^2 \]Plug in \(m = 1.675 \times 10^{-27} \text{ kg}\) and \(c = 3 \times 10^8 \text{ m/s}\):\[ E_0 = 1.675 \times 10^{-27} \times (3 \times 10^8)^2 \approx 1.51 \times 10^{-10} \text{ Joules} \]
05
Calculate the kinetic energy (\(K\))
The kinetic energy \(K\) can be found by subtracting the rest energy from the total energy:\[ K = E - E_0 \]Substituting the values obtained:\[ K \approx 1.06 \times 10^{-9} - 1.51 \times 10^{-10} \approx 9.08 \times 10^{-10} \text{ Joules} \]
06
Verify Units and Logical Consistency
Ensure that all energy values are in Joules and check that the kinetic energy is less than the total energy, as expected for a moving object.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Lorentz_factor
In the world of special relativity, the Lorentz factor, often denoted as \( \gamma \), plays a crucial role. It helps describe how time, length, and relativistic mass change for an object moving close to the speed of light. Here's how it works:
- The Lorentz factor formula is: \[ \gamma = \frac{1}{\sqrt{1 - \frac{v^2}{c^2}}} \]
- "\( v \)" is the velocity of the object, and "\( c \)" is the speed of light.
- As "\( v\)" approaches "\( c\)", the factor "\( \gamma\)" increases significantly, which affects the perceived time and length for the moving object.
rest_energy
Rest energy is another important concept in relativity. It represents the energy stored in an object due to its mass when it is at rest.
- The formula is given by \( E_0 = mc^2 \).
- "\( m\)" is the rest mass of the object, and "\( c\)" is the speed of light.
- This equation, famously derived by Albert Einstein, emphasizes that mass can be seen as a concentrated form of energy.
kinetic_energy
In relativistic physics, kinetic energy is a form of energy that a body possesses due to its motion. It differs from classical kinetic energy in that it factors in the relativistic effects due to high speeds.
- The relativistic kinetic energy is computed by: \[ K = E - E_0 \]
- "\( E\)" is the total energy, while "\( E_0\)" is the rest energy.
- This energy highlights additional energy the object has because it's moving and not just existing.