The angular acceleration of a wheel is given in by where t is in seconds. If the wheel starts from rest at when is the next time the wheel is at rest?
A) 5.1 s
B) 8.4 s
C) 6.9 s
D) 3.6 s
Answer: A
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Bert says that a charged particle in a vacuum can travel in a helix only if a uniform electric field and a uniform magnetic field are both present and both parallel to the axis of the helix. Stuart says that only a magnetic field with a component parallel to the axis of the helix is needed. Which one, if either, is correct, and why?
a. Bert, because the charged particle's velocity can have a vertical component only if an electric field in the vertical direction is present. b. Stuart, because a component of velocity in the vertical direction is not changed by a vertical component of a magnetic field. c. Bert, because a component of velocity in the vertical direction is changed by a vertical component of a magnetic field. d. Stuart, because an electric field in the vertical direction would cause the particle to come to a complete stop. e. Neither, because particles cannot move in helical paths in the presence of magnetic and electric fields.
If we observe one edge of a planet to be redshifted and the opposite edge to be blueshifted, what can we conclude about the planet?
A) The planet is actually two bodies, one moving toward us, the other away from us. B) The planet is in the process of formation. C) The planet is in the process of falling apart. D) The planet is rotating.
The density of air at room temperature is about 1.2 g/cm3. This is the same as
A) 12 kg/m3. B) 120 kg/m3. C) 1200 kg/m3.
You can hear sound through an open window from sources that are not in your line of sight because of
a. interference b. diffraction c. the sound level d. the Doppler effect e. none of the above