A student with a 5.0-kg book bag on her way to class climbs two flights of stairs (a 10-m vertical distance) in 15 s. At what rate did the student do work in carrying the book bag up the stairs?
33 W
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An object 20-cm high is placed 50.0 cm in front of a lens whose focal length is 5.00 cm. Where will the image be located (in cm)?
a. 5.13 b. 5.56 c. 5.72 d. 5.93 e. 4.55
Conduct an analysis to select a material for the skin of an airplane wing. The primary loading of an airplane wing is in bending. During flight, there is low pressure on the top of the wing and high pressure on the wing bottom, bending the wing up. When the plane is stationary on the ground, the weight of the wing bends the wing down. Important parameters for a wing are a high specific elastic modulus, specific tensile yield strength, and specific resistance to fracture. The operating temperature for a wing depends upon the speed of the plane and the altitude. Assume that our plane is subsonic and that the temperature is below 100°C.
(a) Explain what classes of materials can be eliminated from the analysis, based upon the important parameters.
(b) Explain why some materials within acceptable classes can be eliminated based upon important parameters. Why can steel and magnesium alloys be eliminated?
(c) Conduct a numerical analysis of the relative merit of possible materials using the
aluminum alloy 7075-T651, the two conditions of Ti-Al-6V, and carbon-epoxy. These
materials are selected because aircraft wings are made from each of these materials.
The following table presents the elastic modulus (E), yield strength (?y), critical-stress intensity factor (KIc), density (?), and cost (CV) of candidate materials.
These prices are listed prices for metal plate measuring ? in. by 12 in. by 12 in. The
carbon-epoxy is layered laminate from Dragonplate for a sheet of dimensions 0.3175 cm thick by 0.305 m square.
(d) Based upon your results, discuss why Boeing has chosen to use CFRP as the skin
material in the wings of the Boeing 787.
(e) Why don’t more subsonic commercial aircraft producers use this material?
The Kuiper Belt is located just beyond Neptune out to _____
A) 30 AU or less B) 40 AU or less C) 50 AU or more D) 60 AU or more
Briefly describe the characteristics of an elliptical galaxy
What will be an ideal response?