Mineral sample #2 is ________.
Apatite - Ca5(PO4)3(F,Cl,OH)
Corundum - Al2O3
Quartz - SiO2
Quartz - SiO2
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A long wooden rod at 38°C with a 2.5 cm OD is placed into an airstream at 600°C. The heat transfer coefficient between the rod and air is 28.4 W/(m2 K). If the ignition temperature of the wood is 427°C, ? = 800 kg/m3, k = 0.173 W/(m K), and c = 2500 J/(kg K), determine the time between initial exposure and ignition of the wood.
GIVEN
• A long wooden rod is placed into an airstream
• Rod outside diameter (D) = 2.5 cm = 0.025 m
• Initial temperature of the rod (To) = 38°C
• Temperature of the airstream (T?) = 816°C
• The heat transfer coefficient (hc) = 28.4 W/(m2 K)
• The ignition temperature of the wood (TI) = 427°C
• Density of the rod (?) = 800 kg/m3
• Thermal conductivity (k) = 0.173 W/(m K)
• Specific heat (c) = 2500 J/(kg K)
FIND
• The time between initial exposure and ignition of the wood
SKETCH
What kind of asteroid crosses into Earth's orbit?
a. Apollo object b. Amor object c. Centaur asteroids d. Kirkwood objects e. Trojan asteroids
Potential of Point-Charges: A +4.0-?C and a -4.0-?C point charge are placed as shown in the figure. What is the potential difference between points A and B? (k = 1/4??0 = 9.0 × 109 N ? m2/C2)
A. 48 V B. 96 V C. 0 V D. 96 kV E. 48 kV
A man pushes against a rigid, immovable wall. Which of the following is the most accurate statement concerning this situation?
A) The man can never exert a force on the wall which exceeds his weight. B) If the man pushes on the wall with a force of 200 N, we can be sure that the wall is pushing back with a force of exactly 200 N on him. C) Since the wall cannot move, it cannot exert any force on the man. D) The man cannot be in equilibrium since he is exerting a net force on the wall. E) The friction force on the man's feet is directed to the left.