The rate of expansion of the universe is currently increasing
Indicate whether the statement is true or false
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Suppose we imagine the Sun to be about the size of a grapefruit. Which of the following best describes the size and distance of Earth on the same scale?
A) Earth is the size of a tip of a ballpoint pen about 1 meter from the Sun. B) Earth is the size of a golf ball about 1 meter from the Sun. C) Earth is the size of a tip of a ballpoint pen about 15 meters from the Sun. D) Earth is the size of a golf ball about 15 meters from the Sun. E) Earth is the size of a marble about 25 miles from the Sun.
An astronaut goes out for a "space-walk" at a distance above the Earth equal to the radius of the Earth. Her acceleration will be
A) g. B) 1/2 g. C) zero. D) 1/4 g. E) g.
One rad is
a. the amount of radiation that deposits 10?2 J of energy into 1 kg of absorbing material. b. the amount of ionizing radiation that will produce 1/3 × 10^?9 C of electric charge in 1 cm3 of air under standard conditions. c. the amount of radiation needed for ionization of an atom. d. the amount of radiation needed for dissociation of a molecule. e. the amount of radiation that deposits one erg of energy in 1g of material.
The proton-proton chain is
A) the specific set of nuclear reactions through which the Sun fuses hydrogen into helium. B) the linkage of numerous protons into long chains. C) another name for the force that holds protons together in atomic nuclei. D) an alternative way of generating energy that is different from the fusion of hydrogen into helium.