One second after a ball rolls off the edge of a horizontal surface at a speed of 10 m/s,
A) its vertical component of velocity is 10 m/s.
B) its speed is about 14 m/s.
C) both of these
D) none of the above
Answer: C
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An astronomical telescope has an objective of diameter 20 cm with a focal length of 180 cm. The telescope is used with an eyepiece of focal length 3.0 cm. The magnifying power of the telescope is
A) 360 X. B) 60 X. C) 540 X. D) 7 X. E) 180 X.
The surfaces of two concentric spheres having radii of 75 and 100 mm are maintained at 325 K and 275 K, respectively.
(a) If the space between the spheres is filled with nitrogen at 500 kPa, estimate the
convection heat transfer rate.
(b) If both sphere surfaces are black, estimate the total rate of heat transfer between them.
(c) Suggest ways to reduce the heat transfer.
GIVEN
? Concentric spheres with nitrogen between them
? Nitrogen pressure (p) = 500 kPa
? Sphere radii
? Inner sphere (ri) = 75 mm = 0.075 m
? Outer sphere (ro) = 100 mm = 0.1 m
? Sphere temperatures
? Inner sphere (Ti) = 325 K
? Outer sphere (To) = 275 K
? Both spheres are black
FIND
(a) Convective heat transfer (qc)
(b) Total heat transfer (qtotal)
(c) Suggest ways to reduce the heat transfer
ASSUMPTIONS
? Sphere temperatures are constant and uniform
? Only the density of the nitrogen is affected significantly by pressure
? The nitrogen behaves as an ideal gas
PROPERTIES AND CONSTANTS
From Appendix 2, Table 33, for Nitrogen at atmospheric pressure and the mean temperature of 300 K
The density of the nitrogen at 500 kPa can be calculated from the ideal gas law
A ray of light in plastic reaches the edge of the plastic. The medium surrounding the plastic is air and the angle of incidence is larger than the critical angle. What will happen?
A. The ray will refract out of the plastic, bending toward the normal line B. The ray will experience total internal reflection, the angle of reflection being smaller than the angle of incidence C. The ray will experience total internal reflection, the angle of reflection being larger than the angle of incidence D. The ray will refract out of the plastic, bending away from the normal line E. The ray will experience total internal reflection, the angle of reflection equaling the angle of incidence
Beyond the frost line of the solar system, temperatures were low enough for
A) metals to condense into solid form. B) rocks to condense into solid form. C) hydrogen compounds to condense into solid ices. D) asteroids to form. E) hydrogen and helium to condense into ice.