A rock of mass m is dropped to the ground from a height h. A second rock, with mass 3m, is dropped from the same height. When the second rock strikes the ground, its kinetic energy is
1.the same as that of the first rock.
2.three times that of the first rock.
3.six times that of the first rock.
4.nine times that of the first rock.
2
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A heat exchanger wall consists of a copper plate 2 cm thick. The heat transfer coefficients on the two sides of the plate are 2700 and 7000 W/( m2 K), corresponding to fluid temperatures of 92 and 32°C, respectively. Assuming that the thermal conductivity of the wall is 375 W/ ( m K), (a) compute the surface temperatures in °C, and (b) calculate the heat flux in W/ m2.
GIVEN
• Heat exchanger wall, thickness (L) = 2 cm = 0.02 m
• Heat transfer coefficients
? hc1 = 2700 W/(m2 K)
? hc2 = 7000 W/(m2 K)
• Fluid temperatures
? Tf1 = 92°C
? Tf2 = 32°C
• Thermal conductivity of the wall (k) = 375 W/( m K) FIND (a) Surface temperatures (Tw1, Tw1) in °F (b) The heat flux (q/A) in W/m2. ASSUMPTIONS
• One dimensional heat transfer prevails
• The system has reached steady state
• Radiative heat transfer is negligible
SKETCH
An air-filled capacitor is formed from two long conducting cylindrical shells that are coaxial and have radii of 48 mm and 84 mm
The electric potential of the inner conductor with respect to the outer conductor is -400 V. (k = 1/4??0 = 8.99 × 109 N • m2/C2 ) The energy stored in a 1.0-m length of this capacitor is closest to A) 8.0 ?J. B) 5.7 ?J. C) 11 ?J. D) 16 ?J. E) 22 ?J.
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State Kepler's first law of planetary motion
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