Which is not an advantage that a reflector telescope has over a refractor telescope? A. Flaws and bubbles in the material inside a thick mirror are not a problem, while flaws and bubbles in the material inside a thick lens are. B. Reflectors can be built with much bigger apertures. C. The device that collects the light is more easily supported in a reflector. D. Reflectors avoid the problem of chromatic aberration in the lens. E. A reflector doesn’t have to deal with the twinkling of the stars, as a refractor does.

Rank the torques on the five doors shown in the figure above from least to greatest. note that the magnitude of all the forces is the same

Clothing made of several thin layers of fabric with trapped air in between, often called ski clothing, is commonly used in cold climates because it is light, fashionable, and a very effective thermal insulator. so it is no surprise that such clothing has largely replaced thickand heavy old-fashioned coats. (a) consider a jacket made of five layers of 0.1-mm-thick synthetic fabric (k = 0.13 w/m·°c) with 1.5-mm-thick air space (k = 0.026 w/m·°c) between the layers. assuming the inner surface temperature of the jacket to be 28°c and the surface area to be 1.25 m2, determine the rate of heat loss through the jacket when the temperature of the outdoors is 0°c and the heat transfer coefficient at the outer surface is 25 w/m2·°c. (b) what would your response be if the jacket is made of a single layer of 0.5-mm-thick synthetic fabric? what should be the thickness of a wool fabric (k = 0.035 w/m·°c) if the person is to achieve the same level of thermal comfort wearing a thick wool coat instead of a five-layer ski jacket?

What is the force that opposes motion and works against the downward pull? a) friction b) gravity c) weight d) acceleration