Carbon-14 Dating: An archaeologist finds the 14C in a sample of 2.10 g of material to be decaying at 107 Bq. A modern 1.00-g sample of the same material decays at 151 Bq,and assume this rate has also held in the past. The half-life of 14C is 5730 years. How old is the sample?
A. 8980 years
B. 6230 years
C. 17,000 years
D. 8530 years
Answer: A
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Intensity of Sound: At a distance of 15.0 m from a sound source, the intensity level is 60.0 dB. What is the intensity level (in decibels) at a point 2.00 m from the source if the source radiates equally in all directions?
A. 55.7 dB B. 57.5 dB C. 75.5 dB D. 77.5 dB
Water at an average temperature of 27°C is flowing through a smooth 5.08-cm-ID pipe at a velocity of 0.91 m/s. If the temperature at the inner surface of the pipe is 49°C, determine (a) the heat transfer coefficient, (b) the rate of heat flow per meter of pipe, (c) the bulk temperature rise per meter, and (d) the pressure drop per meter.
GIVEN
• Water flowing through a smooth pipe
• Average water temperature (Tw) = 27°C
• Pipe inside diameter (D) = 5.08 cm = 0.0508 m
• Water velocity (V) = 0.91 m/s
• Inner surface temperature of pipe (Ts) = 49°C FIND
(a) The heat transfer coefficient ( h c)
(b) The rate of heat flow per meter of pipe (q/L)
(c) The bulk temperature rise per meter of pipe (?Tw/L)
(d) The pressure drop per meter of pipe (?p/L)
ASSUMPTIONS
• Steady state
• Fully developed flow
SKETCH
PROPERTIES AND CONSTANTS
for water at 27°C
Density (?) = 996.5 kg/m3
Specific Heat (cp) = 4178 J/(kg K)
Thermal conductivity (k) = 0.608 W/(m K)
Absolute viscosity (?) = 845.3 × 10–6 (Ns)/m2
Kinematic viscosity (?) = 0.852 × 10–6 m2/s
Prandtl number (Pr) = 5.8 At the surface temperature of 49°C
Absolute viscosity (?s) = 565.1 × 10–6 (Ns)/m2
A ball rolls across a floor with an acceleration of 0.100 m/s2 in a direction opposite to its velocity. The ball has a velocity of 4.00 m/s after rolling a distance 6.00 m across the floor. What was the initial speed of the ball?
A) 4.15 m/s B) 5.85 m/s C) 4.60 m/s D) 5.21 m/s E) 3.85 m/s
Of the following gases, which is the most important contributor to the Earth's greenhouse effect?
a. water vapor b. ozone c. CFCs d. methane