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Why are we bombarded by muons? Muons are unstable subatomic particles (more on them in Chapter 30) with a mean lifetime of 2.2μs that decay to electrons They are produced when cosmic rays bombard the upper atmosphere about 10 km above the earth’s surface, and they travel very close to the speed of light. The problem we want to address is why we see any of them at the earth’s surface (a) What is the greatest distance a muon could travel during its 2.2 μs lifetime? (b) According to your answer in part (a), it would seem that muons could never make it to the ground. But the 2.μs lifetime is measured in the frame of the muon, and they are moving very fast. At a speed of 0.999c. what is the mean lifetime of a muon as measured by an observer at rest on the earth? How far could the muon travel in this time? Does this result explain why we find muons in cosmic rays? (c) From the point of view of the muon, it still lives for only 2.2 μs, so how does it make it to the ground? What is the thickness of the 10 km of atmosphere through which the muon must travel, as measured by the muon? Is it now clear how the muon is able to reach the ground?
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Chapter 27 Solutions
College Physics (10th Edition)
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University Physics (14th Edition)
Conceptual Integrated Science
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Physics for Scientists and Engineers with Modern Physics
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The Cosmic Perspective (8th Edition)
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- Figure P38.21 shows a jet of material (at the upper right) being ejected by galaxy M87 (at the lower left). Such jets are believed to be evidence of supermassive black holes at the center of a galaxy. Suppose two jets of material from the center of a galaxy are ejected in opposite directions. Both jets move at 0.750c relative to the galaxy center. Determine the speed of one jet relative to the other. Figure P 38.21arrow_forwardThe distance of a galaxy from our solar system is 10 Mpc. (a) What is the recessional velocity of the galaxy? (b) By what fraction is the starlight from this galaxy red shifted (that is, what is its z value)?arrow_forwardWe know that the velocity of an object with mass has an upper limit of c. Is there an upper limit on its momentum? Its energy? Explain.arrow_forward
- On average, how far away are galaxies that are moving away from us at 2.0% of the speed of light?arrow_forwardIn the Check Your Learning section of Example 27.1, the author commented that even at z=0.2 , there is already an 11% deviation between the relativistic and the classical solution. What is the percentage difference between the classical and relativistic results at z=0.1 ? What is it for z=0.5 ? What is it for z=1 ?arrow_forwardParticles called -mesons are produced by accelerator beams. If these particles travel at 2.70108 m/s and live 2.60108 s when at rest relative to an observer, how long do they live as viewed in the laboratory?arrow_forward
- A box is cubical with sides of proper lengths L1 = L2 = L3, as shown in Figure P26.14, when viewed in its own rest frame. If this block moves parallel to one of its edges with a speed of 0.80c past an observer, (a) what shape does it appear to have to this observer? (b) What is the length of each side as measured by the observer? Figure P26.14arrow_forwardIt is year 2120 and we have figure out a propulsion system that allows 0.87c. A first expedition to spaceships travel at velocities as high as v %3D Alpha Centauri (the nearest planetary system) is being planned. Alpha Centauri is 4.3 ly away. Answer the following 5 questions below asking you about the details of this expedition.arrow_forwardEarth's neighboring galaxy, the Andromeda Galaxy, is a distance of 2.54 x 10' light-years from Earth. If the lifetime of a human is taken to be 75.0 years, a spaceship would need to achieve some minimum speed vmin to deliver a living human being to this galaxy. How close to the speed of light would this minimum speed be? Express your answer as the difference between umin and the speed of light c. C- Umin = m/sarrow_forward
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