In a physical fitness program, a woman who weighs 510 N runs up four flights of stairs in 22 s. Each flight rises 3.1 m. (1 hp = 746 W)
(a) What is her total change in potential energy?
(b) What was the minimum average power (in watts) that she expended during the 22 s?
(c) What horsepower motor would be required to generate the same power?
(a) 6.3 kJ (b) 290 W (c) 0.39 hp
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The radioactivity due to carbon-14 measured in a piece of a wood from an ancient site was found to produce 20 counts per minute from a given sample, whereas the same amount of carbon from a piece of living wood produced 160 counts per minute
The half-life of carbon-14, a beta emitter, is 5730 y. The age of the artifact is closest to A) 5700 y. B) 12,000 y. C) 15,000 y. D) 17,000 y. E) 23,000 y.
In using a long steel rod as a lever to move a large rock, where should the fulcrum be placed for a person to use the least amount of force to move the rock?
A. Anywhere in between; it makes no difference B. Close to the rock C. Close to the person D. Exactly halfway between the person and the rock
Suppose a 0.70-kg mass on a spring that has been compressed 0.26 m has elastic potential energy of 2.20 J. How much further must the spring be compressed to triple the elastic potential energy?
a. 0.45 m b. 0.71 m c. 0.78 m d. 0.19 m e. 0.52 m
A uniform rod (length = 2.4 m) of negligible mass has a 1.0-kg point mass attached to one end and a 2.0-kg point mass attached to the other end. The rod is mounted to rotate freely about a horizontal axis that is perpendicular to the rod and that passes through a point 1.0 m from the 2.0-kg mass. The rod is released from rest when it is horizontal. What is the angular velocity of the rod at the
instant the 2.0-kg mass passes through its low point? a. 1.7 rad/s b. 2.2 rad/s c. 2.0 rad/s d. 1.5 rad/s e. 3.1 rad/s