A length of organ pipe is closed at one end. If the speed of sound is 344 m/s, what length of pipe (in cm) is needed to obtain a fundamental frequency of 50 Hz?
a. 28
b. 86
c. 344
d. 172
e. 688
d
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Suppose I push a block along a tabletop at a constant velocity. If I exert a constant forward force of 
on the block and push it through a distance D, I do work on the block equal to ?F?D. Since the block’s kinetic energy does not change, friction must be exerting a backward force on the block of the same magnitude as 
(so that the net force on the block is zero, as required to maintain the block’s constant velocity). What work does the friction force do on the block?
A. No work
B. ? 
D
C. + D
D. Some negative work, but we need more information to determine exactly how much.
E. Some positive work, but we need more information to determine exactly how much.
Before the switch is closed in the figure, the potential across the capacitor is 200 V. At some instant after the switch is closed, the instantaneous current is 0.70 A. What is the energy in the capacitor at this instant?
a.
49 mJ
b.
31 mJ
c.
80 mJ
d.
0.13 J
e.
62 mJ
To send a beam laser-light beam to a space station just above the atmosphere near the horizon, aim your laser
A) above your line of sight. B) below your line of sight. C) along your line of sight.
When a jet airplane takes off, how is momentum conserved?
a. Momentum is conserved because the jet of hot air pushes on the atmosphere around it. b. Momentum is conserved because the air rushing out of the jet engine is moving out in the direction opposite to the plane's movement. c. Momentum is not conserved because the jet was motionless and is now moving. d. Momentum is conserved because molecules in the air move on average in all directions. e. Momentum is conserved because the jet is collecting oxygen from the atmosphere.