Superconductors can carry very large currents with no resistance. If a superconducting wire is formed into a solenoid of length 20.0 cm with 691 turns, what is the magnetic field inside the solenoid when the current is 5.38 kA? (µ0 = 4? × 10^?7 T?m/A)
a. 1.86 T
b. 0.934 T
c. 46.7 T
d. 23.4 T
e. 73.4 T
d
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A rifle is fired straight downward from a high-altitude balloon. If the bullet leaves the barrel at 100 m/s, then its speed one second later (neglecting air resistance) will be about
1) 10 m/s 2) 100 m/s 3) 105 m/s 4) 110 m/s and its distance below will be about 5) 5 m. 6) 100 m. 7) 105 m. 8) 110 m. 9) 120 m.
Which of the following correctly states the number of comets that scientists estimate to be located in the Oort cloud and the number that have actually been observed in the Oort cloud (with telescopes)?
A) estimated number in Oort cloud: 1 trillion observed in Oort cloud: zero B) estimated number in Oort cloud: 1 million observed in Oort cloud: 1,000 C) estimated number in Oort cloud: 100,000 observed in Oort cloud: 50 D) estimated number in Oort cloud: 1 billion observed in Oort cloud: 10,000
Suppose a scientist holds a press conference at which he claims that 10% of the matter in the Milky Way is in the form of dust grains. Does his claim seem reasonable? Why or why not?
A) It is reasonable because we already know that interstellar dust obscures our view through the disk of the galaxy. B) The 10% figure is too high because there are not enough heavy elements to make that much dust. C) It seems reasonable as long as we assume that red giant stars—which produce dust grains in their stellar winds—are more common than we thought. D) The 10% figure is too low because most of the mass of the galaxy is in the form of interstellar dust.
A fire fighter tightens the nut on the top of a fire hydrant using a large wrench. If she applies a force of 250N perpendicular to the wrench, at a point 0.75m from the axis of rotation of the nut, how much work does she do on the nut as she rotates it through 
?
A. 190 J B. 150 J C. 290 J D. 130 J