In a neutron star, the core is:
A) made of compressed neutrons in contact with each other.
B) electrons and protons packed so tightly they are in contact.
C) constantly expanding and contracting.
D) primarily iron and silicon.
E) no longer rotating.
A
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Benzene flowing at 12.5 kg/s is to be cooled continuously from 80°C to 54°C by 10 kg/s of water available at 15.5°C. Using Table 10.6, estimate the surface area required for (a) cross-flow with six tube passes and one shell pass with neither of the fluids mixed and (b) a counterflow exchanger with one shell pass and eight tube passes with the colder fluid inside tubes.
GIVEN
• Benzene coded by water in a heat exchanger
• Benzene flow rate m b= 12.5 kg/s
• Water flow rate m w= 10 mg/s
• Benzene temperatures
? (Tb,in) = 82°C
? (Tb,out) = 54°C
• Water inlet temperature (Tw,in) = 15.5°C
FIND
The surface area required for (a) Cross-flow, 6 tube passes, 1 shell pass, both unmixed (b) Counterflow, 8 tube passes, 1 shell pass, water in tubes
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of water at 20°C (cpw) = 4182 J/(kg K)
the specific heat of Benzene at 68°C (cpb) = 1926 J/(kg K)
Would water molecules in Venus's atmosphere, whose temperature is 740 K, eventually es-cape into outer space? Note that a water molecule has a mass that is 18 times that of a hy-drogen atom. The escape velocity of Venus is 10 km/s. For comparison, a hydrogen atom has an average velocity of 2.5 km/s at a temperature of 300 K.
a. No, the average velocity of water molecules is 0.9 km/s. b. Yes, the average velocity of water molecules is 0.9 km/s. c. Yes, the average velocity of water molecules is 2.1 km/s. d. No, the average velocity of water molecules is 2.1 km/s. e. Yes, the average velocity of water molecules is 19 km/s.
A 20-kg piece of aluminum (which has a specific heat of 900 J/kg • °C) is warmed so that its temperature increases by 5.0°C. How much heat was transferred into it?
a. 4.5 × 10^4 J c. 1.4 × 10^5 J b. 9.0 × 10^4 J d. 2.0 × 10^5 J
Newton's Second Law in 1 Dimension: The figure shows an object's acceleration-versus-force graph. What is the mass of this object?
A. 2.5 g B. 1.6 g C. 630 g D. 400,000 g