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A rocket launched outward from Earth has a speed of 0.100 c relative to Earth. The rocket is directed toward an incoming meteor that may hit the planet. If the meteor moves with a speed of 0.250 c relative to the rocket and directly toward it, what is the velocity of the meteor as observed from Earth?

Short Answer

Expert verified
The velocity of the meteor as observed from Earth is approximately \(-0.154c\).

Step by step solution

01

Understand the Problem

We need to find the velocity of a meteor as observed from Earth, given that the meteor's speed is measured relative to a rocket also moving relative to Earth. We have to use relativistic velocity addition because the speeds involved are significant fractions of the speed of light, denoted as \(c\).
02

Set Known Values

Let the speed of the rocket with respect to Earth be \(v_r = 0.100c\). The speed of the meteor relative to the rocket is \(v_{mr} = 0.250c\). We need to find the meteor's velocity with respect to Earth, \(v_m\).
03

Apply Relativistic Velocity Addition Formula

The formula for relativistic velocity addition is: \[v_m = \frac{v_{mr} + v_r}{1 + \frac{v_{mr} \cdot v_r}{c^2}}\] since both velocities are directed toward each other, we consider the velocity of the meteor as negative when considering it relative to the rocket. Therefore, the actual equation for direct calculation becomes: \[v_m = \frac{-v_{mr} + v_r}{1 - \frac{v_{mr} \cdot v_r}{c^2}}\]
04

Substitute the Values

Substitute \(v_{mr} = 0.250c\) and \(v_r = 0.100c\) into the formula:\[v_m = \frac{-0.250c + 0.100c}{1 - \frac{(0.250c)(0.100c)}{c^2}}\]
05

Simplify the Expression

Simplify the numerator and the denominator:- Numerator: \( -0.250c + 0.100c = -0.150c \)- Denominator: \( 1 - \frac{0.025c^2}{c^2} = 1 - 0.025 = 0.975\)Thus, the expression becomes:\[v_m = \frac{-0.150c}{0.975}\]
06

Calculate the Final Result

Divide the terms to find the velocity of the meteor as observed from Earth:\[v_m = -0.1538c\]This negative sign indicates it is moving towards Earth.

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Key Concepts

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

Special Relativity
Special relativity, a groundbreaking theory proposed by Albert Einstein in 1905, revolutionized our understanding of physics by introducing the concept that the laws of physics are the same for all non-accelerating observers. According to this theory, the speed of light in a vacuum is a universal constant, denoted as \( c \), approximately equal to 299,792,458 meters per second. One of the fascinating aspects of special relativity is how it changes our understanding of time and space when objects move at significant fractions of the speed of light.
The principle that time and space are intertwined is key to understanding relativistic effects, such as time dilation and length contraction. Time dilation means that time appears to pass more slowly for objects moving close to the speed of light compared to stationary observers. Length contraction implies that objects in motion appear shorter along the direction of motion from the perspective of a stationary observer.
By using the principles of special relativity, we can solve complex physics problems involving high velocities, like the velocities of spaceships or meteors in our everyday physics problems.
Velocity of Light
The velocity of light is a fundamental constant in physics. In special relativity, it plays a critical role as the ultimate speed limit of the universe. No material object, signal, or information can travel faster than this speed. This constraint fundamentally affects how we measure and understand the motion of objects at high velocities. The speed of light, \( c \), is not just another number; it is a boundary that ensures the consistency of the laws of physics.
When objects move at speeds significant relative to the speed of light, traditional Newtonian velocity addition becomes inaccurate. This is because, at high speeds, velocities do not simply add up. Instead, we employ the relativistic velocity addition formula to find the resultant velocity between two moving observers. This formula helps accurately account for the effects of special relativity. It ensures the result lies within the physical limits imposed by the speed of light, preventing any resultant speed from exceeding \( c \).
Understanding this concept allows us to correctly interpret scenarios involving high-speed interactions, such as those described in our exercise involving rockets and meteors.
Physics Problem Solving
Solving physics problems often requires a strategic approach to break down a real-world scenario into manageable parts. This discipline involves identifying known values, applying appropriate physical laws or formulas, and calculating the unknowns.
For the exercise about observing the meteor from Earth, problem-solving begins with recognizing the relevance of special relativity due to the significant speeds involved. This means we can't use simple arithmetic for velocity. Instead, we use the relativistic velocity addition formula. This formula, \[ v_m = \frac{-v_{mr} + v_r}{1 - \frac{v_{mr} \cdot v_r}{c^2}} \], adjusts for the effects of light-speed limits by considering each velocity's impact on the other.
Breaking down the problem into steps:
  • Identify the velocities and their relation to each observer.
  • Substitute known values (such as \( v_{mr} = 0.250c \) and \( v_r = 0.100c \)) into the formula.
  • Simplify and calculate to find the observed velocity from Earth.
Such systematic approaches ensure accurate solutions and a better understanding of complex physics problems.

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Most popular questions from this chapter

If the Sun became a black hole, what would be its average density, assuming it to be a sphere with a radius equal to the Sun's Schwarzschild radius? Compare your answer to the actual average density of the Sun.

An electron is accelerated to a speed of \(1.50 \times 10^{8} \mathrm{~m} / \mathrm{s}\) At that speed, compare the relativistic results to the classical results for (a) the electron's kinetic energy, (b) its total energy, and (c) the magnitude of its momentum. (d) What is its rest energy classically? Relativistically?

Roughly speaking, the observable mass in our universe is all attributed to stars and gas clouds in the galaxies. (a) Assuming that each galaxy contains the mass of 200 billion Suns and there are 200 billion such galaxies, what is the Schwarzschild radius of the universe? (b) Modern observations indicate that there is much more mass in the universe than can be "seen," in the form of "dark matter," neutrinos, etc. Suppose that the actual mass of the universe was 100 times larger than the visible mass. What would the Schwarzschild radius be under those conditions? (c) Current observations place the lifetime of the universe at about 13 billion years. Compare the distance light can travel in this time to your answer from part (b). Can you conclude anything about the universe itself being a black hole?

An astronaut in a spacecraft moves past a field \(100 \mathrm{~m}\) long (according to a person standing on the field) and parallel to the field's length at a speed of \(0.75 c\) (a) Will the length of the field, according to the astronaut, be (1) longer than \(100 \mathrm{~m},\) (2) equal to \(100 \mathrm{~m},\) or (3) shorter than \(100 \mathrm{~m}\) ? Why? (b) What is the length as measured by the astronaut? (c) Which length is the proper length?

Alpha Centauri, a star close to our solar system, is about 4.3 light-years away. Suppose a spaceship traveled this distance at a constant speed of \(0.90 c\) relative to Earth. (a) How long did the trip take according to an Earth- based clock? (b) How long did the trip take according to the traveler's clock? Which of you answers to parts (a) and (b) are proper time intervals, if any? (c) What is the trip distance according to an Earth-based observer? (d) What is the trip distance according to the traveler? Which of your answers to parts (b) and (c) are proper lengths, if any?

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