A stable group of stars that formed and are held together by their combined gravity is called a stellar association
Indicate whether the statement is true or false
False
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Processes in which one type of quark is converted into another type of quark involve which force?
a. electromagnetic b. strong force c. weak force d. gravitational
A spherical mirror has a radius of curvature of 22 cm. If the mirror is concave, its focal length is
A) -11 cm. B) -22 cm. C) 11 cm. D) -44 cm. E) 22 cm.
The voltage between two parallel plates separated by a distance of 3.0 cm is 120 V. The electric field between the plates is
A) 3.6 V/m. B) up to 4000 V/m depending on position. C) 2000 V/m halfway between the plate. D) 4000 V/m. E) 7.2 V/m.
A long steel rod (2 cm in diameter, 2-m-long) has been heat-treated and quenched to a temperature of 100°C in an oil bath. To cool the rod further, it is necessary to remove it from the bath and expose it to room air. Will the faster cool-down result from cooling the cylinder in the vertical or horizontal position? How long will the two methods require to allow the rod to cool to 40°C in 20°C air?
GIVEN • A long steel rod in air • Diameter (D) = 2 cm = 0.02 m • Length (L) = 2 m • Initial temperature (Ts,i) = 100°C • Air temperature (T?) = 20°C FIND (a) Is it faster to cool the rod vertically or horizontally? (b) Time for rod to cool to 40°C in each position ASSUMPTIONS • Steel is 1% carbon PROPERTIES AND CONSTANTS for 1% carbon steel Thermal conductivity (ks) = 43 W/(m K) Specific heat (c) = 473 J/(kg K) Density (?) = 7801 kg/m3 for dry air at the initial mean temperature of 60°C Thermal expansion coefficient (?) = 0.003 1/K Thermal conductivity (k) = 0.0279 W/(m K) Kinematic viscosity (?) = 19.4 × 10–6 m2/s Prandtl number (Pr) = 0.71