The Paleozoic era began about how many million years ago?
a. 65
b. 545
c. 245
d. 3
b
You might also like to view...
The rate of cratering
A) has remained constant over the last 4.6 billion years. B) has recently increased with more collisions in the asteroid belt. C) fluctuates over time, with massive bodies occasionally coming in from the Oort Cloud. D) shows that large asteroid impacts are more common now than in the past. E) shows that most interplanetary debris was swept up soon after the formation of the solar system.
Two charges, Q1 and Q2, are separated by a certain distance R. If the magnitudes of the charges are halved, and their separation is also halved, then what happens to the electrical force between these charges?
A) It increases by a factor of 16. B) It increases by a factor of 8. C) It is doubled. D) It is quadrupled. E) It remains the same.
Ohmic heating is
a. always undesirable. b. used in light bulbs. c. what makes fuses "blow". d. all of the above.
You are standing on a platform and a train approaches you, moving at a constant velocity. Its whistle is blowing continuously. The train does not stop at the platform, but it continues to move past the platform at a constant velocity. Which of the following statements are true about the frequency of the train's whistle that you hear?
1.The whistle's frequency that you hear increases continually as the train approaches the platform and then decreases continually after the train passes the platform. 2.The whistle's frequency that you hear seems to you to remain constant for the entire duration of the train's passage. 3.The whistle's frequency that you hear decreases continually as the train approaches the platform and then increases continually after the train passes the platform. 4.The whistle's frequency that you hear remains constant as the train approaches the platform and then decreases immediately after the train passes the platform, after which it remains constant at a lower pitch than it had originally.