The force per unit area exerted by an electromagnetic wave is called the
A)
energy density.
B)
power.
C)
intensity.
D)
radiation pressure.
E)
radiation field.
D
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Which of the following is suggested as the best explanation of the missing solar neutrinos?
a. The sun is fusing helium but not hydrogen. b. Nuclear reactions do not produce neutrinos as fast as theory predicts. c. The sun may contain matter we haven't yet identified. d. Neutrinos may oscillate between three different flavors. e. None of the above
Observations indicate that over billions of years, galaxies in general tend to change from
A) smaller and bluer to larger and redder. B) larger and redder to smaller and bluer. C) smaller and redder to larger and bluer. D) larger and bluer to smaller and redder.
You and a classmate are discussing how much work one must do to lift a box of mass m a vertical distance h. Your classmate argues, “You have to exert an upward force on the box at least equal in magnitude to the box’s weight 
, and you lift the box upward a distance h, so you must do work equal to 
. But in addition,” your classmate continues, “ you must increase the box’s gravitational potential energy by 
to lift the box.” What amount of work do you think you need to do on the box to lift it a height h? Be prepared to defend your response. (Hint: What is the system here?)
A. Zero work
B. About 
(if you move the box slowly)
C. Significantly greater than 
but less than 
D. About 
(if you move the box slowly)
E. Significantly greater than 
A circular cylinder of height 1.20 m having faces of diameter 0.620 m is immersed in water of density 1.00 × 10^3 kg/m3 with its axis vertical so that its faces are parallel to the surface of the water. The upper face is 2.50 m below the surface of the water. The net force on this cylinder is observed to be 1120 N downward. Atmospheric pressure is 1.01 × 10^5 Pa. What is the weight of the cylinder?
A) 7.40 × 10^3 N B) 1.09 × 10^4 N C) 3.79 × 10^4 N D) 4.14 × 10^4 N E) 1.37 × 10^5 N