100 grams of liquid nitrogen at 77 K is stirred into a beaker containing 200 grams of 5°C water. If the nitrogen leaves the solution as soon as it turns to gas, how much water freezes? (The heat of evaporation of nitrogen is 6.09 cal/gram and the heat of fusion of water is 80 cal/gram.)
What will be an ideal response?
none
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Write the energy balance for an ice pond at noon on a sunny day with solar energy of 300 W/m2 to the ice, air at -8ºC, convective heat transfer coefficient of 10 W/m^2?K above the ice, and 1ºC water with a convective heat transfer coefficient of 30 W/m^2?K below the ice. Then estimate the rate at which the ice thickness is increasing or decreasing.
What will be an ideal response?
Opacity is
a. the balance between the pressure and force of gravity inside a star. b. the force that binds protons and neutrons together to form a nucleus. c. the force that binds an electron to the nucleus in an atom. d. a measure of the resistance to the flow of radiation (photons) through a gas. e. the temperature and density at which a gas will undergo thermonuclear fusion.
The following four forces act on a 4.00 kg object: 1 = 300 N east 2 = 700 N north 3 = 500 N west 4 = 600 N south What is the acceleration of the object?
A) 224 N in a direction 63.4° north of west B) 300 N in a direction 63.4° north of west C) 300 N in a direction 26.6° north of west D) 224 N in a direction 26.6° north of west E) 2100 N in a direction 26.6° north of west
In what sense are the quasars "quasi-stellar"?
A) Their energy production is hydrogen-helium fusion, like main sequence stars. B) They are upscale versions of O stars, yet hundreds of times more massive. C) Their luminosity comes from the millions of supergiants that compose them. D) Their spectra is like that of ordinary stars. E) In short time exposures, their images looked stellar.