Why are planetary magnetic fields important?
A. They protect the planet from impacts.
B. They help prevent the loss of a planet's atmosphere.
C. They counteract tidal forces.
D. They keep the planet rotating.
Answer: B
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Red giant stars are I. more luminous than the sun. II. larger in diameter than the sun. III. cooler than B stars. IV. located above the main sequence stars in the H-R diagram
a. I & II b. II & IV c. I, II, & IV d. II, III, & IV e. I, II, III, & IV
A 4,000 kg satellite is traveling in a circular orbit 200 km above the surface of the Earth. A 3.00 gram marble is dropped inside the satellite. What is the acceleration of the marble as viewed by the observers on the Earth? 
A. 9.80 
B. 9.24
C. 8.90
D. 8.62
E. 7.95
The greatest gravitational lensing is produced by the ________ that lie in the centers of massive galaxies
Fill in the blank(s) with correct word
A system of an electron, a proton, and a neutron has a net charge of
a. +1.6 × 10^-19 C. b. –1.6 × 10^-19 C. c. 3.2 × 10^-19 C. d. zero.