A body is oscillating up and down at the end of a spring. Let's consider when the body is at the top of its up and down motion. Two cars crash head on. At any given time during the crash, the magnitudes of the collision forces exerted on each car are exactly equal. This is an example of Newton's
a. first law c. third law
b. second law d. no law
C
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One method of storing solar energy for use during cloudy days, or at night, is to store it in the form of sensible heat in a rock bed. Suppose such a rock bed has been heated to 70°C and it is desired to heat a stream of air by blowing it through the bed. If the air inlet temperature is 10°C and the mass velocity of the air in the bed is 0.5 kg/(s m2), how long must the bed be in order for the initial outlet air temperature to be 65°C? Assume that the rocks are spherical, 2 cm in diameter, and that the bed void fraction is 0.5. (Hint: The surface area of the rocks per unit volume of the bed is (6/Dp)(1 –(?).)
GIVEN
Packed bed of rocks with air blowing through it
Initial temperature of rocks (Tr) = 70°C
Inlet air temperature (Ta,in) = 10°C
Mass velocity of air (m/A) = 0.5 kg/(s m2)
Outlet air temperature (Ta,out) = 65°C
Surface area per unit volume (As/V) = (6/Dp)(1 –(?) )
FIND
Length of bed required (L)
ASSUMPTIONS
Rocks are spherical with diameter (D) = 2 cm = 0.02 m
Void fraction of the bed (?) = 0.5
Rock temperature remains practically constant
SKETCH
A heat engine that in each cycle does positive work and loses energy as heat, with no heat energy input, would violate:
A. the zeroth law of thermodynamics B. the first law of thermodynamics C. the second law of thermodynamics D. the third law of thermodynamics E. Newton's second law
The index of refraction for a certain material is 1.399 for red light and 1.432 for blue light. Light containing both of these colors is traveling in vacuum and strikes a flat sheet of this material
Find the angle separating the two colors in the refracted light in the sheet if the angle of incidence is 60.00°.
At the moment of a total eclipse, the moon lies along a line from the Earth to the sun. If your normal weight is 600 N, how much is your weight decreased by the combined pull of the sun and moon? MSUN = 2.0 × 10^30 kg, rS-E = 1.5 × 10^8 km MMOON = 7.4 × 10^22 kg, rM-E = 3.8 × 10^5 km