The outward pressure of hot gas in the Sun
A) is balanced by the inward gravitational pressure.
B) is increasing the Sun's diameter.
C) is cooling the photosphere.
D) is responsible for variations in the sunspot cycle.
E) weakens the magnetic field.
A
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Why isn’t the crust of Venus broken into mobile plates as Earth’s crust is? How do you know?
a. Venus’s crust is much thicker and denser than Earth’s, so that probably prevents the crust from breaking. Moreover, there are no shield volcanoes on Venus. b. The mantle of Venus consists of great amounts of sulfur and fluorine, which makes mantle substances more solid and less plastic. So there are no traces of magma eruptions on Venus. c. Strong winds in the dense atmosphere of Venus sufficiently get rid of the interior heat, so there are no interior currents of matter to drive plate motion. Moreover, there are no shield volcanoes on Venus. d. Low-density, dryness, and pliability of Venus’s crust probably prevented it from breaking into rigid plates. On Venus there are no chains of composite volcanoes that form at plate boundaries.
Equilibrium: An athlete holds a 7.5-kg shot put in his hand with his lower arm horizontal, as shown in the figure. His lower arm has a mass of 2.8 kg and its center of gravity (or center of mass) is 12 cm from the elbow-joint pivot. How much force must the extensor muscle (which is
M in the figure) in the upper arm exert on the lower arm?
A. 100 N B. 500 N C. 1000 N D. 1500 N
A long wire carrying a 2.0-A current is placed along the y-axis. What is the magnitude of the magnetic field at a point 0.60 m along the x-axis?
A) 6.7 × 10-7 T B) 13 × 10-7 T C) 1.2 × 10-7 T D) 6.7 T E) 12 T
The root mean square speed of a gas molecule is greater than the average speed, because the former gives a greater weight to
a. lighter molecules. b. heavier molecules. c. lower speeds. d. higher speeds. e. more probable speeds.