Energy and Mass: How many MeV of energy is released during a reaction in which 1.67 × 10-25 kg of material is converted to energy? (c = 3.0 × 108 m/s, 1 eV = 1.67 × 10-19 J)
A. 5.0 × 10-14 MeV
B. 4.1 × 10-7 MeV
C. 3.1 × 10-4 MeV
D. 9.4 × 104 MeV
Answer: D
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Fermium-253 has a half-life of 3.00 d. A sample of fermium contains 7.37 × 107 nuclei. How long will it take for there to be only 3.36 × 106 fermium nuclei in this sample?
A) 2.75 d B) 9.80 d C) 13.4 d D) 15.7 d E) 58.6 d
What causes the outward gas pressure that balances the inward pull of gravity in a main-sequence star?
a. the rapid outward flow of gas b. the rapid inward flow of the gas c. the high temperature of the gas d. the high density of the gas e. the high temperature and the high density of the gas
In two-dimensional collisions momentum conservation is
A. In the x or y direction, but not both B. In both the x and y directions C. In the y direction only D. In the x direction only
To reduce the home heating requirements, modern building codes in many parts of the country require the use of double-glazed or double-pane windows, i.e., windows with two panes of glass. Some of these so called thermopane windows have an evacuated space between the two glass panes while others trap stagnant air in the space. (a) Consider a double-pane window with the dimensions shown in the sketch given below. If this window has stagnant air trapped between the two panes and the convective heat transfer coefficients on the inside and outside surfaces are 4 W/(m2 K) and 15 W/(m2 K), respectively, calculate the overall heat transfer coefficient for the system. (b) If the inside air temperature is 22°C and the outside air temperature is –5°C, compare the heat loss through a 4 m2
double-pane window with the heat loss through a single-pane window. Comment on the effect of the window frame on this result. (c) If the total window area of a home heated by electric resistance heaters at a cost of $.10/kWh is 80 m2 how much more cost can you justify for the double-pane windows if the average temperature difference during the six winter months when heating is required is about 15°C?
GIVEN
- Double-pane window with stagnant air in gap
- Convective heat transfer coefficients
- Air temperatures
FIND
(a) The overall heat transfer coefficient
(b) Compare heat loss of double- and single-pane window
(c) Cost to justify for the use of double-pane window.
ASSUMPTIONS
- Steady state conditions prevail
- Radiative heat transfer is negligible
SKETCH
