If a radioactive element has a half-life of 5760 years, and the amount of parent material remaining is one-fourth of the original amount, the specimen is about
A) 11,520 years old.
B) 17,280 years old.
C) 23,040 years old.
D) 28,800 years old.
Answer: A
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A puck on a frictionless air hockey table has a mass of 5.0 kg and is attached to a cord passing through a hole in the surface as in the figure. The puck is revolving at a distance 2.0 m from the hole with an angular velocity of 3.0 rad/s. The angular momentum of the puck (in kg?m2/s) is 
A. 80 B. 20 C. 30 D. 60 E. 50
An enclosed chamber with sound absorbing walls has a 2.0 m × 1.0 m opening for an outside window. A loudspeaker is located outdoors,, 78 m away and facing the window
The intensity level of the sound entering the window space from the loudspeaker is 79 dB. Assume the acoustic output of the loudspeaker is uniform in all directions and that the acoustic energy incident upon the ground is completely absorbed and therefore is not reflected into the window. The threshold of hearing is 1.0 × 10-12 W/m2. The acoustic power entering through the window space is closest to A) 160 µW. B) 79 µW. C) 320 µW. D) 790 µW. E) 1600 µW.
Adiabatic Processes: A certain ideal gas has a value of the adiabatic constant ? = 4/3. What is the molar specific heat at constant pressure of this gas in terms of R?
A. 5R/2 B. 2R C. 3R D. 7R/2 E. 4R
A 320-kg satellite experiences a gravitational force of 800 N. What is the radius of the satellite's orbit? (Earth's radius is 6,400 km.)
A. 6,400 km B. 12,800 km C. 19,200 km D. 25,600 km