Mean Life: The decay rate of a radioactive sample decreases from 175 kBq to 12.4 kBq in 18.3 s. What is the mean life (time constant) of this sample?
Fill in the blank(s) with the appropriate word(s).
6.91 s
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Assume that all air properties may be evaluated at 27°C and determine the constants in the correlation equation: Nu = C (Gr Pr)m
A laboratory experiment has been performed to determine the natural-convection heat
transfer correlation for a horizontal cylinder of elliptical cross section in air. The
cylinder is 1-m-long, has a hydraulic diameter of 1 cm, a surface area of 0.0314 m2, and
is heated internally by electrical resistance heating. Recorded data include power
dissipation, cylinder surface temperature, and ambient air temperature. The power
dissipation has been corrected for radiation effects:
GIVEN
• A horizontal, elliptical cylinder in air
• Hydraulic diameter (Dh) = 1 cm = 0.01 m
• Length (L) = 1 m
• Cylinder surface area (As) = 0.0314 m2
• Experimental data for (Ts – T?) and q shown above FIND
• The constants in the correlation equation Nu = C(Gr Pr)m
ASSUMPTIONS
• All air properties may be evaluated at 27°C
SKETCH
PROPERTIES AND CONSTANTS
for dry air at 27°C
Thermal expansion coefficient (?) = 0.00333 1/K
Thermal conductivity (k) = 0.0256 W/(m K)
Kinematic viscosity (?) = 16.4 × 10–6 m2/s
Prandtl number (Pr) = 0.71
You and a classmate are discussing how much work one must do to lift a box of mass m a vertical distance h. Your classmate argues, “You have to exert an upward force on the box at least equal in magnitude to the box’s weight 
, and you lift the box upward a distance h, so you must do work equal to 
. But in addition,” your classmate continues, “ you must increase the box’s gravitational potential energy by 
to lift the box.” What amount of work do you think you need to do on the box to lift it a height h? Be prepared to defend your response. (Hint: What is the system here?)
A. Zero work
B. About 
(if you move the box slowly)
C. Significantly greater than 
but less than 
D. About 
(if you move the box slowly)
E. Significantly greater than 
The angle of rotation between the ends of a nylon bar is 3.58. The bar diameter is 70 mm and the allowable shear strain is 0.014 rad. The minimum permissible length of the bar is approximately:
(A) 0.15 m
(B) 0.27 m
(C) 0.40 m
(D) 0.55 m
Bacteria are examples of
A) unicellular prokaryotes B) unicellular eukaryotes C) multicellular eukaryotes D) multicellular prokaryotes