If the headlights on a car are separated by 1.3 m, how far down the road can they be resolved if the angular resolution of the eye is 5.0 × 10-4 rad and the person has excellent vision?
A) 1.3 km
B) 5.0 km
C) 4.8 km
D) 0.65 km
E) 2.6 km
E
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Photons of light can be absorbed by an atom of an element ____
a. if they match one of several possible wavelengths that are absorbed by that element b. if they match one of several possible wavelengths that are absorbed by all elements c. if they match the only particular wavelength that can be absorbed by that element d. if they match the only particular wavelength that can be absorbed by all elements e. no matter what wavelength they have
Acceleration: Suppose that a car traveling to the east (+x direction) begins to slow down as it approaches a traffic light. Which statement concerning its acceleration must be correct?
A. Its acceleration is in the +x direction. B. Its acceleration is in the -x direction. C. Its acceleration is zero. D. Its acceleration is decreasing in magnitude as the car slows down.
A mid-ocean ridge is formed at the boundary of two plates
a. that are separating from one another. b. that are sliding horizontally past one another. c. where one is pushing over the top of the other. d. that are basically at rest.
While flowing at the rate of 1.25 kg/s in a simple counterflow heat exchanger, dry air is cooled from 65 to 38°C by means of cold air which enters at 15°C and flows at a rate of 1.6 kg/s. It is planned to lengthen the heat exchanger so that 1.25 kg/s. of air can be cooled from 65 to 26°C with a counterflow current of air at 1.6 kg/s entering at 15°C. Assuming that the specific heat of the air is constant, calculate the ratio of the length of the new heat exchanger to the length of the original.
GIVEN
A simple adiabatic air-to-air counter flow heat exchanger:
Case 1
? Warm air temperatures
? Th,in = 65°C
? Th,out = 38°C
? Air flow rates
? mh = 1.25 kg/s
? mc = 1.6 kg/s
? Cold air inlet temperature (Tc,in) = 15°C
After lengthening heat exchanger:
Case 2
? Warm air temperatures
? Th,in = 65°C
? Th,out = 26°C
? Air flow rates
? mh = 1.25 kg/s
? mc = 1.6 kg/s
? Cold air inlet temperature (Tc,in) = 15°C
FIND
? The ratio of the length of the new heat exchanger to the length of the original
ASSUMPTIONS
? The specific heat of air is constant
? The overall heat transfer coefficient (U) is the same in both cases
SKETCH
