Careful measurements reveal that a star maintains a steady apparent brightness at most times, except that at precise intervals of 73 hours the star becomes significantly dimmer for about 2 hours. The most likely explanation is that
A) the star is a member of an eclipsing binary star system.
B) the star is a Cepheid variable.
C) the star is periodically ejecting gas into space, every 73 hours.
D) the star is a white dwarf.
A) the star is a member of an eclipsing binary star system.
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Ganymede has many features that look like its history may be similar to the Earth's Moon's, but with water on Ganymede playing the role of rock on the Moon
Indicate whether the statement is true or false
Is any force exerted on you when you slow down while moving along a straight line?
A) No, no force acts as long as you are slowing down. B) Yes, there is a force on you but it is impossible to state the direction of this force because the question contains insufficient information. C) Yes, there is a backward force on you, opposite to your direction of motion. D) Yes, there is a forward force on you, along your direction of motion. E) Yes, there is a sideways force on you.
Two experimental runs are performed to determine the calorimetric properties of an alcohol which has a melting point of -10° C
In the first run, a 200-g cube of frozen alcohol, at the melting point, is added to 300 g of water at 20°C in a styrofoam container. When thermal equilibrium is reached, the alcohol-water solution is at a temperature of 5°C. In the second run, an identical cube of alcohol is added to 500 g of water at 20°C and the temperature at thermal equilibrium is 10°C. The specific heat capacity of water is 4190 J/kg ? K. Assume no heat is exchanged with the styrofoam container and the surroundings. What is the specific heat capacity of the alcohol? A) 1700 J/kg ? K B) 1900 J/kg ? K C) 2100 J/kg ? K D) 2300 J/kg ? K E) 2500 J/kg ? K
A microscope has an objective lens of focal length 1.40 mm and an eyepiece of focal length 20.00 mm. It is adjusted for minimum eyestrain for persons with a near point of 25.0 cm. A blood sample is placed 1.50 mm from the objective
How far apart are the lenses? A) 20 mm B) 21 mm C) 23 mm D) 41 mm