The abundance of oxygen and ozone in Earth's atmosphere can be explained only through biology
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TRUE
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Buoyancy: When a container of water is placed on a laboratory scale, the scale reads 120 g. Now a 20-g piece of copper (of density 8.9 g/cm3) is suspended from a thread and lowered into the water, not touching the bottom of the container. What will the scale now read? The density of water is 1.0 g/cm3.
A. 120 g B. 122 g C. 138 g D. 140 g
Two objects of the same mass move along the same line in opposite directions. The first mass is moving with speed v
The objects collide, stick together, and move with speed 0.100v in the direction of the velocity of the first mass before the collision. What was the speed of the second mass before the collision? A) 1.20v B) 10.0v C) 0.900v D) 0.800v E) 0.00v
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
An object whose center of gravity is below its point of support, will be in neutral equilibrium
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