The percentage (by mass) of the Sun that is Hydrogen is about:
A) 91%.
B) 71%.
C) 27%.
D) 9%.
E) less than 1%.
B
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Light travels at speed c. Complete the following equation using only words: wave speed = _____________ × ________________
Fill in the blank(s) with correct word
Galaxy A and galaxy B formed at the same time. Galaxy A is much farther from us than galaxy B. Which of the following is true?
A) Galaxy A will appear younger to us than galaxy B. B) Galaxy A will appear older to us than galaxy B. C) Galaxy A will appear to be the same age as galaxy B.
You are racing away from Earth in a super spaceship in which you can continually increase your speed. Which of the following best explains how people on Earth will perceive your speed?
A) They will know you are going very fast but will have no way of knowing whether you ever exceed the speed of light. B) You will see any beam of light from Earth coming toward you at the speed of light, which means it will catch you. Thus, the people on Earth must conclude that you are going slower than the speed of light. C) An imaginary spaceship can go as fast as it wants, so the folks on Earth soon will see you going faster than the speed of light. D) You may soon be racing away from Earth faster than the speed of light, but, if so, people on Earth will no longer be able to see you. E) Without more information, it is impossible to know how fast you would see a light beam from Earth coming toward you. If it happens that you are going fast enough so that the light can't catch you, then people on Earth would find you to be going faster than light.
An electron is accelerated from rest through a potential difference of 3.75 kV. It enters a region where a uniform 4.0-mT magnetic field is perpendicular to the velocity of the electron
Calculate the radius of the path this electron will follow in the magnetic field. (e = 1.60 × 10-19 C, melectron = 9.11 × 10-31 kg) A) 1.2 cm B) 2.2 cm C) 3.2 cm D) 4.2 cm E) 5.2 cm