In the late 1800s, Kelvin and Helmholtz suggested that the Sun stayed hot because of gravitational contraction. What was the major drawback to this idea?
A) It predicted that the Sun could shine for about 25 million years, but geologists had already found that Earth is much older than this.
B) It predicted that the Sun would shrink noticeably as we watched it, but the Sun appears to be stable in size.
C) It is physically impossible to generate heat simply by making a star shrink in size.
D) It predicted that Earth would also shrink in size with time, which would make it impossible to have stable geology on our planet.
A) It predicted that the Sun could shine for about 25 million years, but geologists had already found that Earth is much older than this.
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Entropy: A 0.42-kg quantity of ethanol, in the liquid state at its melting point of -114.4°C, is frozen at atmospheric pressure. The heat of fusion of ethanol is 1.04 × 105 J/kg, and its molecular mass is 46.1 g/mol. What is the change in the entropy of the ethanol as it freezes?
A. -280 J/K B. -250 J/K C. -310 J/K D. 250 J/K E. 280 J/K
Work Done by a Gas: A gas expands at constant temperature from an initial volume of 0.040 m3 and an initial pressure of 210 kPa until its pressure drops to 135 kPa. How much work is done by the gas during this expansion? (R = 8.31 J/mol ? K)
A. 3.0 kJ B. 3.7 kJ C. 4.1 kJ D. 5.6 kJ E. 7.9 kJ
A 6.0-kg object moving 2.0 m/s in the positive x direction has a one-dimensional elastic collision with a 4.0-kg object moving 3.0 m/s in the opposite direction. What is the total kinetic energy of the two-mass system after the collision?
A. 30 J B. 62 J C. 20 J D. 44 J E. 24 J
Cal is viewing the Moon with his new telescope, using a 10-mm focal length eyepiece. For greater detail, he wishes to double the magnification of his telescope
An eyepiece having which one of the following characteristics will accomplish this for him? A) 40 diopters B) 8 mm C) 12 mm D) 200 diopters E) 5 diopters