Imagine hitting a heavy anvil with a hammer. The hammer is in contact with the metal for a short period of time. How do you suppose the time of contact depends upon how hard you hit the anvil (i.e
, does a hard hit remain in contact much longer or shorter than a light tap?) [It is reasonable to assume Hooke's law of elasticity to hold.]
The anvil has an effective elastic constant which is relatively large. The time of contact does NOT depend upon the strength of the blow. The PERIOD of oscillation (the time in contact is half a period!) is independent of the amplitude for SHM.
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A section of a composite wall with the dimensions shown below has uniform temperatures of 200°C and 50°C over the left and right surfaces, respectively. If the thermal conductivities of the wall materials are: kA = 70 W/(m K), kB = 60 W/(m K), kc = 40 W/(m K) and kD = 20 W/(m K), determine the rate of heat transfer through this section of the wall and the temperatures at the interfaces. including a contact resistance of 0.1 K/W at each of the interfaces.
GIVEN
• Composite wall
• Thermal conductivities:
? kA = 70 W/(m K)
? kB = 60 W/(m K)
? kC = 40 W/(m K)
? kD = 20 W/(m K)
• Surface temperatures
? Left side (TAs) = 200°C
? Right side (TDs) = 50°C
• Contact resistance at each interface (Ri) = 0.1 K/W FIND
(a) Rate of heat transfer through the wall (q) (b) Temperatures at the interfaces
ASSUMPTIONS
• One dimensional conduction
• The system is in steady state
SKETCH
A supplier wants to make a profit by buying gold by weight at one altitude and selling it at the same price per newton at another altitude. The supplier should
A) buy at a high altitude and sell at a low altitude. B) buy at a low altitude and sell at a high altitude. C) disregard altitude because it makes no difference.
Ultraviolet light is shone on a piece of metal that has a known work function, and electrons are observed being produced through the interaction of the light with the metal. The lamp that produces the light is now replaced with a lamp of the same intensity, but which produces photons having a shorter wavelength. What difference is observed in the number of electrons produced per unit time?
A. The same number are produced. B. Fewer are produced . C. Without knowing more about the wavelengths used, one cannot answer. D. More are produced.
A 60-vibration-per-second wave travels 30 meters in 1 second. Its frequency is
A) 30 hertz and it travels at 60 m/s. B) 60 hertz and it travels at 30 m/s. C) 1800 hertz and it travels at 2 m/s. D) none of the above