________ are small dark nebulae about 1 light-year in diameter that contain 10 to 1,000 solar masses
a. HI regions
b. HII regions
c. Emission nebulae
d. Bok globules
e. Reflection nebulae
d
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Suppose an object is hanging from the end of a spring. Let the spring’s length when the object is hanging at rest be L. Now suppose we pull the object downward until the spring has been stretched a length of 2L. By what factor has the force that the spring is exerting on the object increased?
A. The spring force is the same in both cases.
B. 
times stronger
C. 2 times stronger
D. 4 times stronger
E. The answer depends on the spring’s relaxed length.
_________is the degradation of a material because of electrochemical reactions with its environment.
Fill in the blank(s) with the appropriate word(s).
A 2.0-kg object moving 3.0 m/s strikes a 1.0-kg object initially at rest. Immediately after the collision, the 2.0-kg object has a velocity of 1.5 m/s directed 30° from its initial direction of motion. What is the y component of the velocity of the 1.0-kg object just after the collision?
A. ?3.7 m/s B. ?3.4 m/s C. ?1.5 m/s D. ?2.4 m/s E. ?4.1 m/s
A circuit consists of N resistors, all of resistance R, connected as shown below. A potential difference V is applied to the circuit. The equivalent resistance of the circuit is
A.
.B.
.C.
D.
E.