Earth's magnetic field is generated in the iron-rich mantle
a. True
b. False
Indicate whether the statement is true or false
False
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When an elevator is accelerating upward, the frequency of a pendulum inside
A) increases. B) decreases. C) doesn't change.
A 3.0-kg block slides on a frictionless 20° inclined plane. A force of 16 N acting parallel to the incline and up the incline is applied to the block. What is the acceleration of the block?
a. 2.0 m/s2 down the incline b. 5.3 m/s2 up the incline c. 2.0 m/s2 up the incline d. 3.9 m/s2 down the incline e. 3.9 m/s2 up the incline
How does the density of copper at its melting point of 1356 K compare to that of copper at room temperature, 293 K? Its linear expansion coefficient is 
?
A. 1.054 times as large B. 1.018 times as large C. 0.946 times as large D. 0.982 times as large E. 0.947 times as large
What makes us think that Mars must once have had an atmosphere that was warmer and had higher surface pressure?
A) The atmosphere is too cold and thin for liquid water today, yet we see evidence of flowing water in the past. B) We think it for purely theoretical reasons, based on calculations showing that the Sun has brightened with time. C) The presence of inactive volcanoes on Mars tells us that there must once have been a lot of outgassing, and hence a thicker atmosphere. D) The fact that parts of Mars have a lot of craters tell us that Mars must once have been much warmer.