A lathe, initially at rest, accelerates at 0.60 rad/s2 for 10 s, then runs at a constant angular velocity for 20 s, and finally decelerates uniformly for 10 s to come to a complete stop. What is its average angular velocity?
A)
4.5 rad/s
B)
3.5 rad/s
C)
5.0 rad/s
D)
3.0 rad/s
E)
4.0 rad/s
A
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The horizontal component of the buttressing force at the base of a pointed arch is
A) less than that of a rounded arch. B) equal to that of a rounded arch. C) greater than that of a rounded arch. D) zero in magnitude.
Simple harmonic oscillations can be modeled by the projection of circular motion at constant angular velocity onto a diameter of the circle. When this is done, the analog along the diameter of the acceleration of the particle executing simple harmonic motion is
a. the displacement from the center of the diameter of the projection of the position of the particle on the circle. b. the projection along the diameter of the velocity of the particle on the circle. c. the projection along the diameter of tangential acceleration of the particle on the circle. d. the projection along the diameter of centripetal acceleration of the particle on the circle. e. meaningful only when the particle moving in the circle also has a non-zero tangential acceleration.
Why are fossils of early life on Earth rarer than fossils of plants and animals from the past few hundred million years?
A) We find fossils in sedimentary layers, and no sediments were deposited until just a few hundred million years ago. B) Life was far less abundant prior to a few hundred million years ago. C) Early organisms were microscopic and lacked skeletons and other hard structures that are most likely to be fossilized. D) Fossils could not form before there was oxygen in the atmosphere.
Polarization is a property of
A) transverse waves. B) longitudinal waves. C) both of these D) neither of these