Exam 1 Solutions_F24 PHYS-222 PDF

## EXAM 1 - FALL 2024 ### PHYS-222 1. About how many kilometers is 15 light years? - 3E+5 km - 3.2E+7 km - 1.4E+14 km - 9.5E+15 km - No answer, one is a unit of time and other is a distance. 2. Newton's laws are a good approximation of relativistic laws at low velocities......

## EXAM 1 - FALL 2024 ### PHYS-222 1. About how many kilometers is 15 light years? - 3E+5 km - 3.2E+7 km - 1.4E+14 km - 9.5E+15 km - No answer, one is a unit of time and other is a distance. 2. Newton's laws are a good approximation of relativistic laws at low velocities... - in inertial reference frames - always - in non-inertial frames - only within our solar system - never 3. A clock in a spaceship is observed to run at a speed of only 3/5 that of a similar clock at rest on Earth. How fast is the spaceship moving? - 9/10c - 4/5c - 3/5c - 2/5c - 1/5c 4. A spaceship of length 40m when at rest is observed to be 20m long when in motion. How fast is it moving? - 1.7c - 0.86c - 0.75c - 0.68c - 0.48c 5. Galilean Invariance means... - that if Newton's laws are valid in one reference frame, then they are also valid in another reference frame moving at a constant velocity relative to the first system. - the same as Newtonian Principle of Relativity. - that the Newton's laws are invariant in inertial reference frames. - (a) and (b) - (a), (b), and (c) 6. What was the significance of the Michelson & Morley experiment? - It helped dis-prove the existence of the Ether and forced reconsideration of the nature of light. - It proved the existence of the Ether and explained all behavior of light. - It laid the basis for quantum physics. - It directly laid the mathematical basis for general relativity. - The Michelson & Morley experiment was not significant. 7. This information relates to the next three questions. Suppose some astronauts traveled from the earth to a far planet and back a total distance of 4 light years, and the trip took 7 years as measured on earth. Assuming (incorrectly) that they moved with a constant velocity. (Hint: 1 light year is the distance that light travels in 1 year.) - What was the relativistic factor γ? - 1.12 - 1.22 - 1.32 - 1.42 - 1.52 - What was the time experienced by the astronaut for the trip? - 6.01 years - 5.74 years - 5.00 years - 4.72 years - 2.02 years - What was the time difference for the trip between the clocks on earth and their clocks? - 1.4 years - 1.26 years - 1.1 years - 0.83 years - 0y, there was no measurable difference in time. 8. A spaceship is traveling towards the earth at 0.60c relative to the earth when it launches a space probe. The space probe accelerates towards to the earth and quickly reaches a speed of 0.9c relative to the spaceship. What is the speed of the probe relative to the earth? - 0.63c - 0.85c - 0.91c - 0.97c - 1.5c 9. An observer on earth watches a spacecraft moving at 0.8c pass overhead. Shortly after passing over, a piece of litter from the rocket is thrown back at 0.7c relative to the spacecraft. What is the speed of the litter relative to the earth? - 0.1c - 0.23c - 0.75c - 0.71c - 0.96c 10. An observer on earth watches a spacecraft moving at 0.8c pass overhead. Shortly after passing over, the spacecraft shoots a missile forward at 0.7c relative to the spacecraft. What is the speed of the missile relative to the earth? - 0.23c - 0.96c - 0.1c - 0.75c - 0.71c 11. A spacecraft traveling away from us out of the solar system at a speed of 0.84c sends back information at a rate of 700Hz. At what rate do we receive the information? - 103 Hz - 206 Hz - 309 Hz - 407 Hz - 813 Hz 12. A star outputs orange light with a frequency fo of 493.9 THz. It is moving towards the earth blue shift direction at a speed of 0.032c. What is the frequency f of light as seen from an observer on earth? - purple (689.2 THz) - blue (618.1 THz) - yellow light (509.9 THz) - Orange-red (478.1 THz) - red (442.2 THz) 13. Which is the best description for why we need modern physics? - Classical physics does not fully describe the behavior of objects moving at relativistic speeds, nor of objects of atomic size and smaller such as electrons. - There is no need for modern physics. - Classical physics was old. - Classical physics is incomplete due to a lack of explanation for things like chemical reactions and unified forces. - Modern physics describes physics discovered between 1900 and 1950. 14. Two spaceships are traveling towards each other at relativistic speeds. The first spaceship is traveling at v₁ = 0.3c relative to an observer on earth, and the second spaceship is traveling at v2 = 0.5c relative to an observer on earth. What speed does the second spaceship see the first spaceship travel at? - 0.40c - 0.50c - 0.60c - 0.70c - 0.80c 15. A particle initially has a speed of 0.5 c. At what speed does its momentum increase by 50%? - 0.803c - 0.750c - 0.667c - 0.550c - 0.500c 16. By how much would the rest energy of a proton change if it was accelerated to c? - It would not change. - It would grow to infinity. - It would change by gamma. - It would drop to zero. - It would become undefined. 17. During lecture we looked at the binding energy of the deuteron atom (2H) we neglected to include the binding energy of the electron in the calculations. Why could this be done? - The binding energy of the electron was several magnitudes less than the binding energy of the proton and neutron. - The electron does not have binding energy. - The electron binding energy is much greater than those of the proton and neutron, but we only cared about the binding energy of the nucleus so it did not count. - The electron binding energy is perfectly balanced and does not contribute to the atomic binding energy. - The deuteron atom does not contain an electron. 18. An approximately 30m long pendulum is placed on a planet with about 3 times earth's gravity (assume gearth = 10m/s²). What would be the period of a single swing? (T = 2π√(l/g)) - 10 s - 6 s - 5 s - 3 s - 1 s