A 2-kg ball is moving with a constant speed of 5 m/s in a horizontal circle whose radius is 50 cm. What is the acceleration of the ball?
A)
0 m/s2
B)
10 m/s2
C)
20 m/s2
D)
50 m/s2
E)
500 m/s2
D
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The graph above shows 4 models for how the average distance between galaxies could change with time, from the past (left) to now (middle) to the future (right-hand side). The graph also shows real data, based on white dwarf supernovae. Which model predicts that galaxies had the largest separations in the past?
A) accelerating B) coasting C) critical D) recollapsing
Weight and g: From what height above the surface of the earth should an object be dropped to initially experience an acceleration of 0.54g? (G = 6.67 × 10-11 N ? m2/kg2, Mearth = 5.97 × 1024 kg, Rearth = 6.38 × 106 m)
A. 2300 km B. 1700 km C. 5400 km D. 2900 km
Water flowing at a rate of 12.6 kg/s is to be cooled from 90 to 65°C by means of an equal flow rate of cold water entering at 40°C. The water velocity with the such that the overall coefficient of heat transfer U is 2300 W/(m2 K). Calculate the heat-exchanger surface area (in square meters) needed for each of the following arrangements: (a) parallel flow, (b) counterflow, (c) a multi-pass heat exchanger with the hot water making one pass through a well-baffled shell and the cold water making two passes through the tubes, and (d) a crossflow heat exchanger with both sides unmixed.
GIVEN
• Warm water cooled by cold water in a heat exchanger
• Both flow rates ( m c) = 12.6 kg/s
• Water temperatures
? Th,in = 90°C
? Th,out = 65°C
? Tc,in = 40°C
• Overall heat transfer coefficient (U) = 2300 W/(m2 K)
FIND
The transfer area (A) for (a) Parallel flow (c) Tube-and-shell; 1 hot shell pass, 2 cold tube passes (b) Counterflow (d) Crossflow–both unmixed
ASSUMPTIONS
• The specific heat is constant
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of water in the temperature range of interest (cp) = 4187 J/(kg K)
Fundamental Forces: How does the range of an exchange force depend on the mass of the exchange particle?
A. The range is longer for a massive exchange particle than for a light exchange particle. B. The range is shorter for a massive exchange particle than for a light exchange particle. C. The range does not depend on the mass of the exchange particle.