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.
B
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Fill in the blank(s) with correct word
Metals that do not recrystallize during hot-working have a high ___________rate.
Fill in the blank(s) with the appropriate word(s).
After 8.0 years have elapsed, 15/16 of a sample of a specific radionuclide has decayed. What is the half-life of the radionuclide?
A cylindrical liquid oxygen (LOX) tank has a diameter of 1.22 m, a length of 6.1 m, and hemispherical ends. The boiling point of LOX is – 179.4°C. An insulation is sought which will reduce the boil-off rate in the steady state to no more than 11.3 kg/h. The heat of vaporization of LOX is 214 kJ/kg. If the thickness of this insulation is to be no more than 7.5 cm, what would the value of its thermal conductivity have to be?
GIVEN
• Insulated cylindrical tank with hemispherical ends filled with LOX
• Diameter of tank (Dt) = 1.22 m
• Length of tank (Lt) = 6.1 m
• Boiling point of LOX (Tbp) = –179.40C
• Heat of vaporization of LOX (hfg) = 214 kJ/kg
• Steady state boil-off rate ( m ) = 11.2 kg/h
• Maximum thickness of insulation (L) = 7.5 cm = 0.075 m
FIND
The thermal conductivity (k) of the insulation necessary to maintain the boil-off rate below 11.2 kg/h. ASSUMPTIONS
• The length given includes the hemispherical ends
• The thermal resistance of the tank is negligible compared to the insulation
• The thermal resistance at the interior surface of the tank is negligible
SKETCH
