A 4.0-kg mass, initially at rest on a horizontal frictionless surface, is struck by a 2.0-kg mass moving along the x axis with a speed of 8.0 m/s. After the collision, the 2.0-kg mass has a speed of 4.0 m/s at an angle of 37° from the positive x axis. What is the speed of the 4.0-kg mass after the collision?
A. 2.0 m/s
B. 2.7 m/s
C. 4.9 m/s
D. 2.4 m/s
E. 3.6 m/s
Answer: B
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Air at an average temperature of 150°C flows through a short square duct 10 × 10 × 2.25 cm at a rate of 15 kg/h. The duct wall temperature is 430°C. Determine the average heat transfer coefficient, using the duct equation with appropriate L/D correction. Compare your results with flow-over-flat-plate relations.
GIVEN
• Air flowing through a short square duct
• Average air temperature (Ta) = 150°C
• Duct dimensions = 10 × 10 × 2.25 cm = 0.1 × 0.1× 0.0225 m
• Duct wall surface temperature (Ts) = 430°C
• Mass flow rate (m ) = 15 kg/h
FIND
The average heat transfer coefficient ( h c) using (a) The duct equation with appropriate L/D correction (b) The flow-over-flat-plate relation
ASSUMPTIONS
• Constant and uniform duct wall temperature
SKETCH
PROPERTIES AND CONSTANTS
for dry air at the average temperature of 150°C
Thermal conductivity (k) = 0.0339 W/(m K)
Absolute viscosity (?b) = 23.683 × 10–6 (Ns)/m2
Prandtl number (Pr) = 0.71 At the surface temperature of 430°C,
the absolute viscosity (?s) = 33.66 × 10–6
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The theory proposing light as a particle is supported by
1.the sparks created in Hertz' experiment with the spark gap oscillator. 2.the speed of light turning up in Maxwell's equations. 3.the interference caused by light in Young's double slit experiment. 4.the photoelectric effect Hertz discovered.
A 2 000-kg sailboat experiences an eastward force of 3 000 N by the ocean tide and a wind force against its sails of magnitude 6 000 N directed toward the northwest (45° N of W). What is the magnitude and direction of the resultant acceleration?