Dust particles are pulverized rock, which has density 2500 kg/m3. They are approximately spheres 20 ?m in diameter
Treating dust as an ideal gas, what is the root-mean-square speed (thermal speed) of a dust particle at 400°C? (The Boltzmann constant is 1.38 × 10-23 J/K.) A) 5.2 × 10-5 m/s
B) 1.7 × 10-5 m/s
C) 3.0 × 10-5 m/s
D) 7.3 × 10-5 m/s
A
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In a single-pass counterflow heat exchanger, 1.25 kg/s of water enter at 15°C and cools 2.5 kg/s of an oil having a specific heat of 2093 J/(kg K) from 95°C to 65°C. If the overall heat transfer coefficient is 280 W/(m2 K), determine the surface area required.
GIVEN
• Water cooling oil in a single-pass counterflow heat exchanger
• Water flow rate ( m w)= 1.25 kg/s
• Oil flow rate ( m o)= 2.5 kg/s
• Oil specific heat (cpo) = 2093 J/(kg K)
• Water inlet temperature (Tw, in) = 15°C
• Oil temperature
? To, in = 95°C
? To, out = 65°C
• Overall heat transfer coefficient (U) = 280 W/(m2 K)
FIND
• The surface area (A) required
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of water (cpw) = 4187 J/(kg K)
A car travels at 15 m/s for 10 s. It then speeds up with a constant acceleration of 2.0 m/s2 for 15 s. At the end of this time, what is its velocity?
A) 15 m/s B) 30 m/s C) 45 m/s D) 375 m/s
How many moles of sugar, C12H22O11, are there in 200. grams?
A) 0.585 moles B) 68,400 moles C) 1.71 moles D) 0.684 moles
The composition of Mercury's crust is:
A) deficient in volatile compounds that contain elements such as sulfur and potassium. B) consistent with material from the solar wind, indicating that Mercury has collected material over the last few billion years. C) similar to the crust of the other terrestrial planets. D) nearly identical to Mercury's mantle material.