A pure sample of 226Ra contains 2.0 × 10^14 atoms of the isotope. If the half-life of 226Ra = 1.6 × 10^3 years, what is the decay rate of this sample? (1 Ci = 3.7 × 10^10 decays/s)
7.4 × 10^-8 Ci
You might also like to view...
Wave Characteristics: A radio station broadcasts at 80 MHz. How long does it take for this radio signal to travel a distance of 2.0 × 107 m through space? (c = 3.0 × 108 m/s)
A. 0.15 × 10-2 s B. 15 ms C. 6.7 × 10-2 s D. 20 ms E. 25 ms
The refrigeration system for an indoor ice rink is to be sized by an HVAC contractor. The refrigeration system has a COP (coefficient of performance) of 0.5. The ice surface is estimated to be –2°C and the ambient air is 24°C. Determine the size of the refrigeration system in kW required for a 110 m diameter circular ice surface.
GIVEN
? Round ice rink
? Diameter (D) = 110 m
? Ice surface temperature (Ts) = – 2°C
? Air temperature (T?) = 24°C
? COP of refrigeration system = 0.5
FIND
? Size of the refrigeration system required
ASSUMPTIONS
? Air is quiescent
? The effects of sublimation are negligible
? Radiation heat transfer is negligible
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 28, for dry air at the mean temperature of 11°C
A deep space probe moving forward in space needs to make a course correction and so fires a thruster on the side of the probe 90° away from its direction of motion, as shown below. This thruster, while on, exerts a constant force on the probe perpendicular to its original direction of motion. While the thruster is operating, which trajectory best describes the probe’s motion? (Hint: Note that the thrust force delivers an upward impulse to the probe during every successive time interval. Consider what happens to the ball in figure C2.4 as it receives analogous continual downward impulses.)
A. A
B. B
C. C
D. D
E. E
In a shell of a shell and tube heat exchanger with two shell passes and eight tube passes, 12.6 kg/s of water is heated in the shell from 800C to 150°C. Hot exhaust gases having roughly the same physical properties as air enter the tubes at 340°C and leave at 180°C. The total surface, based on the outer tube surface, is 930 m2 . Determine (a) the log-mean temperature difference if the heat exchanger were simple counterflow type, (b) the correction factor F for the actual arrangement, (c) the effectiveness of the heat exchanger, (d) the average overall heat transfer coefficient.
GIVEN
• A tubular heat exchanger with 2 shell passes and 8 tube passes
• Water in the shell, exhaust gases in the tubes
• Exhaust gases have roughly the same physical properties as air
• Water flow rate m w= 12.6 kg/s
• Water temperatures
? Tw,in = 80°C
? Tw,out = 150°C
• Exhaust temperatures
? Te,in = 340°C
? Te,out = 180°C
• Surface are (A) = 930 m2
FIND
(a) LMTD if the exchanger is a simple counterflow type
(b) Correction F for the actual arrangement
(c) Effectiveness (e)
(d) The overall heat transfer coefficient (U)
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of water at the mean temperature of 130°C (cpw) = 4244.5 W/(kg K)