A set of twins, Andrea and Courtney, are initially 10 years old. While Courtney remains on Earth, Andrea rides on a spaceship that travels away from Earth at a speed of 0.60c for 10 years (as measured by Courtney)
At the end of the trip, Courtney is 20 years old. How old is Andrea? A) 10 years
B) 12 years
C) 18 years
D) 20 years
C
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The Earth is able to recover from a snowball phase by
A) the gradual melting of snow and ice by solar radiation B) the gradual buildup of heat beneath the snow and ice layer C) the breaking up of the snow and ice layer by plate tectonics D) carbon dioxide gradually building up in the atmosphere from volcanism
What is a rem?
A) A rem is a unit for measuring radiation exposure. B) A rem is the maximum exposure limit for occupational safety. C) Rem stands for Rapid Electron Motion. D) A rem is the number of radiation particles absorbed per second. E) Rem is an '80s rock group.
What is the correct fraction of dust to gas in the interstellar medium?
a. 1/99 b. 10/90 c. 50/50 d. 90/10
The force of Earth's gravity on a capsule in space increases as it comes closer. When the capsule moves to half its distance, the force toward Earth is then
A) twice. B) three times greater. C) four times greater. D) none of the above