A policeman walks on his beat back and forth. His average speed is determined from
A. time divided by how far he ends up from the starting point.
B. his velocity divided by the time.
C. time divided by his total distance covered.
D. his total distance covered divided by the time.
Answer: D
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Two marbles are rolling along parallel tracks (which may or may not be inclined). A stroboscopic photograph showing a top view of the positions of the marbles at equally spaced instants of time looks like this: At what instant(s) of time do the marbles have the same instantaneous velocity?
A. At time tB
B. At time tG
C. At both tB and tG
D. Some instant between tC and tD
E. Some instant between tD and tE
F. Roughly time tD
Briefly explain how a fiber made of oriented ultra-high-molecular-weight polyethylene can be much stronger than structural steel in tension, but perpendicular to the fiber axis, its hardness is much less than that of steel.
What will be an ideal response?
Faraday's Law: A flat coil having 40 turns, each one of cross-sectional area 12.0 cm2, is oriented with its plane perpendicular to a uniform magnetic field. The field varies steadily from 0.00 T to 1.20 T in 20.0 ms. What emf is induced in the coil during this time?
Fill in the blank(s) with the appropriate word(s).
What prevents a brown dwarf from undergoing nuclear fusion?
A) Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion. B) There is not enough mass to maintain nuclear reactions in a self-sustaining way. C) The surface temperature never rises high enough for the radiation to be trapped and heat their interior to the temperatures required for nuclear fusion. D) Radiation pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion. E) There are too many heavy elements and not enough hydrogen for fusion to occur in a self-sustaining way.