Nuclear Binding Energy: In massive stars, three helium nuclei fuse together, forming a carbon nucleus, and this reaction heats the core of the star. The net mass of the three helium nuclei must therefore be
A. higher than that of the carbon nucleus.
B. less than that of the carbon nucleus.
C. the same as that of the carbon nucleus because mass is always conserved.
D. the same as that of the carbon nucleus because energy is always conserved.
Answer: A
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An aluminum cantilever beam (E 5 72 GPa) with a square cross sec-tion and span length L 5 2.5 m is subjected to uniform load q 5 1.5 kN/m. The allowable bending stress is 55 MPa. The maximum deflection of the beam is approximately:
(A) 10 mm
(B) 20 mm
(C) 30 mm
(D) 40 mm
Find the wavelength of the photon emitted during the transition from the second EXCITED state to the ground state in a harmonic oscillator with a classical frequency of 3.72 × 1013 Hz
(c = 3.00 × 108 m/s, 1 eV = 1.60 × 10-19 J, h = 1.055 × 10-34 J ? s, h = 6.626 × 10-34 J ? s) A) 4.03 ?m B) 2.26 ?m C) 2.98 ?m D) 5.24 ?m
Dark energy was discovered as astronomers studied
A) black holes. B) the motion of galaxies within galactic clusters. C) redshift of distant galaxies. D) weakly interacting massive particles.
A shell-and-tube heat exchanger is to be used to cool 25.2 kg/s of water from 38°C to 32°C. The exchanger has one shell-side pass and two tube side passes. The hot water flows through the tubes and the cooling water flows through the shell. The cooling water enters at 24°C and leaves at 32°C. The shell-side (outside) heat transfer coefficient is estimated to be 5678W/(m 2 K). Design specifications require that the pressure drop through the tubes be as close to 13.8 kPa as possible and that the tubes be 18 BWG copper tubing (1.24 mm wall thickness), and each pass is 4.9 m long. Assume that the pressure losses at the inlet and outlet are equal to one and one half of a velocity heat (?V2/gc), respectively. For these specifications, what tube diameter and how many tubes are needed?
GIVEN
A water-to-water shell-and-tube exchanger, hot water in tubes, cooling water in shell One shell and two tube passes Hot water flow rate m
h= 25.2 kg/s Water temperatures
? Hot: Th,in = 38°C Th,out = 32°C
? Cold: Tc,in = 24°C Tc,out = 32°C Shell-side transfer coefficient h o= 5678 W/(m2 K) Pressure drop (?p) = 13.8 kPa Tube wall thickness (t) = 1.24 mm = 0.00124 m Tube length per pass (Lp) = 4.9 m
FIND
The tube diameter (Do) and number of tubes (N)
ASSUMPTIONS
Pressure losses at inlet and outlet (?pii) = 1.5 (? V2/gc) Variation of thermal properties with temperature is negligible Fouling resistance is negligible Thermal resistance of the tube walls is negligible
SKETCH
PROPERTIES AND CONSTANTS
for water at 30°C Density (?) = 995.7 kg/m3
Specific heat (cp) = 4176 J/(kg K)
Thermal conductivity (k) = 0.615 W/(m K)
Kinematic viscosity (?) = 0.805 × 10–6 m2/s
Prandtl number (Pr) = 5.4