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An imperial spaceship, moving at high speed relative to the planet Arrakis, fires a rocket toward the planet with a speed of 0.920c relative to the spaceship. An observer on Arrakis measures that the rocket is approaching with a speed of 0.360c. What is the speed of the spaceship relative to Arrakis? Is the spaceship moving toward or away from Arrakis?

Short Answer

Expert verified
The spaceship's speed is approximately \(-0.961c\) and it is moving towards Arrakis.

Step by step solution

01

Identify Known Values

First, recognize the given values: \( v_{rs} = 0.920c \), which is the velocity of the rocket relative to the spaceship, and \( v_{rp} = -0.360c \), which is the velocity of the rocket relative to the planet Arrakis (negative because it is approaching the planet). We are tasked with finding \( v_{sp} \), the velocity of the spaceship relative to Arrakis.
02

Set Up the Relativistic Velocity Addition Formula

Use the relativistic velocity addition formula: \[ v_{rp} = \frac{v_{rs} + v_{sp}}{1 + \frac{v_{rs} v_{sp}}{c^2}} \]. Substitute \( v_{rs} = 0.920c \) and \( v_{rp} = -0.360c \) into the formula.
03

Solve for the Velocity of the Spaceship

Rearrange the formula to solve for \( v_{sp} \): \[ v_{sp} = \frac{v_{rp} - v_{rs}}{1 - \frac{v_{rp} v_{rs}}{c^2}} \]. Substitute \( v_{rp} = -0.360c \) and \( v_{rs} = 0.920c \) into the equation: \[ v_{sp} = \frac{-0.360c - 0.920c}{1 - \frac{-0.360c \times 0.920c}{c^2}} \].
04

Calculate the Spaceship's Velocity

Simplify the expression: \[ v_{sp} = \frac{-1.28c}{1 + 0.3312} \]. This simplifies to \[ v_{sp} = \frac{-1.28c}{1.3312} \]. Calculate the value: \[ v_{sp} \approx -0.961c \].
05

Interpret the Result

The negative sign in \( v_{sp} = -0.961c \) indicates that the spaceship is moving towards Arrakis. The speed relative to Arrakis is approximately \( 0.961c \).

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Key Concepts

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

special relativity
Special relativity is an important concept in physics, introduced by Albert Einstein in 1905. It focuses on how the laws of physics are the same for all non-accelerating observers, and it introduces key ideas about the nature of space and time. One of its most significant implications is that the speed of light in a vacuum, denoted as \( c \), is constant and is the absolute speed limit for any object in the universe.
Special relativity has several core principles, including time dilation and length contraction, but one of its more practical applications is calculating velocities when objects are moving at a significant fraction of the speed of light. Unlike simple addition used in classical mechanics, these calculations require a more complex formula known as the relativistic velocity addition formula. This formula helps predict how observers in different frames of reference perceive the speed of moving objects. Understanding these concepts is crucial for physicists working with high-speed particles, such as those in particle accelerators or objects moving through space.
Einstein's theory of relativity
Einstein's theory of relativity is composed of two parts—special relativity and general relativity. Special relativity deals with objects moving at constant speeds, particularly those close to the speed of light. This theory revolutionized how we understand time and space, showing that they are intertwined in what we call spacetime.
In practical terms, special relativity affects how velocities add up. Unlike classical physics, where speeds simply add together, Einstein's insights revealed that as objects move faster, especially close to the speed of light, their mass effectively increases and time behaves differently. This requires using the relativistic velocity addition formula to combine velocities accurately.
  • The formula ensures no combined velocity exceeds the speed of light, preserving the implications of relativity.
  • It explains phenomena observed in high-speed travel and deep space exploration.
  • It underpins technologies like GPS, where accurate timekeeping is essential due to the effects on time dilation.
By comprehending these insights, one can better appreciate the cosmic speed limit imposed by light and the intriguing mechanics of space travel.
spaceship velocity calculation
To determine the velocity of the spaceship moving relative to Arrakis, we use the relativistic velocity addition formula. This formula is critical when dealing with velocities close to the speed of light, as seen in the exercise where both the rocket and spaceship are traveling at significant fractions of \( c \).
The formula applied is:
\[v_{rp} = \frac{v_{rs} + v_{sp}}{1 + \frac{v_{rs} v_{sp}}{c^2}}\],
where:
  • \( v_{rp} \) represents the velocity of the rocket relative to the planet Arrakis, given as \(-0.360c\).
  • \( v_{rs} \) is the velocity of the rocket relative to the spaceship, given as \(0.920c\).
  • \( v_{sp} \) is what we need to find—the velocity of the spaceship relative to Arrakis.
By rearranging and solving this equation, one can determine \( v_{sp} \). Substitution and calculation yield \(-0.961c\), indicating the spaceship moves towards Arrakis, with a high velocity reflecting the combined effects of the rocket's speed and the spaceship's own motion in space.
physics problem solving
Physics problem-solving, especially in the realm of relativistic physics, requires a methodical approach.
For the spaceship velocity calculation, the problem can be broken down systematically:
  • Identifying known values: Assess what information is given (e.g., velocities relative to different references).
  • Choosing the appropriate formula: In relativistic contexts, opting for the relativistic velocity addition rather than classical methods.
  • Rearranging formulas: To solve for the desired quantity, such as the spaceship's speed relative to a reference frame.
  • Substituting values and simplifying expressions to find a clear numerical solution.
Understanding the step-by-step process can demystify seemingly complex relativistic problems. It combines fundamental concepts of special relativity with mathematical manipulation to gain insights into physical phenomena. Such problem-solving techniques are essential for students and professionals handling real-world physics challenges, undeniably enhancing their analytical skills.

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Most popular questions from this chapter

If a muon is traveling at 0.999c, what are its momentum and kinetic energy? (The mass of such a muon at rest in the laboratory is 207 times the electron mass.)

As you have seen, relativistic calculations usually involve the quantity \(\gamma\). When \(\gamma\) is appreciably greater than 1, we must use relativistic formulas instead of Newtonian ones. For what speed \(v\) (in terms of \(c\)) is the value of \(\gamma\) (a) 1.0% greater than 1; (b) 10% greater than 1; (c) 100% greater than 1?

Inside a spaceship flying past the earth at three-fourths the speed of light, a pendulum is swinging. (a) If each swing takes 1.80 s as measured by an astronaut performing an experiment inside the spaceship, how long will the swing take as measured by a person at mission control (on earth) who is watching the experiment? (b) If each swing takes 1.80 s as measured by a person at mission control, how long will it take as measured by the astronaut in the spaceship?

Many of the stars in the sky are actually \(binary\space stars\), in which two stars orbit about their common center of mass. If the orbital speeds of the stars are high enough, the motion of the stars can be detected by the Doppler shifts of the light they emit. Stars for which this is the case are called \(spectroscopic\space binary\space stars. \textbf{Figure P37.68}\) shows the simplest case of a spectroscopic binary star: two identical stars, each with mass \(m\), orbiting their center of mass in a circle of radius \(R\). The plane of the stars' orbits is edge-on to the line of sight of an observer on the earth. (a) The light produced by heated hydrogen gas in a laboratory on the earth has a frequency of 4.568110 \(\times\) 10\(^{14}\) Hz. In the light received from the stars by a telescope on the earth, hydrogen light is observed to vary in frequency between 4.567710 \(\times\) 10\(^{14}\) Hz and 4.568910 \(\times\) 10\(^{14}\) Hz. Determine whether the binary star system as a whole is moving toward or away from the earth, the speed of this motion, and the orbital speeds of the stars. (\(Hint\): The speeds involved are much less than \(c\), so you may use the approximate result \(\Delta f/f = u/c\) given in Section 37.6.) (b) The light from each star in the binary system varies from its maximum frequency to its minimum frequency and back again in 11.0 days. Determine the orbital radius \(R\) and the mass \(m\) of each star. Give your answer for \(m\) in kilograms and as a multiple of the mass of the sun, 1.99 \(\times\) 10\(^{30}\) kg. Compare the value of \(R\) to the distance from the earth to the sun, 1.50 \(\times\) 10\(^{11}\) m. (This technique is actually used in astronomy to determine the masses of stars. In practice, the problem is more complicated because the two stars in a binary system are usually not identical, the orbits are usually not circular, and the plane of the orbits is usually tilted with respect to the line of sight from the earth.)

The French physicist Armand Fizeau was the first to measure the speed of light accurately. He also found experimentally that the speed, relative to the lab frame, of light traveling in a tank of water that is itself moving at a speed \(V\) relative to the lab frame is $$v = {c \over n} + kV$$ where \(n\) = 1.333 is the index of refraction of water. Fizeau called \(k\) the dragging coefficient and obtained an experimental value of \(k\) = 0.44. What value of \(k\) do you calculate from relativistic transformations?

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