Process of Science: Explain how we can use telescopes as time machines to directly test theories of galaxy formation
What will be an ideal response?
Telescopes see objects as they were when the light left them. For distant objects, this "lookback time" can be billions of years and we can literally see galaxies in the process of formation. In this way, we can directly test theories for how they form.
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Estimate the rate of convective heat transfer across a 1-m-tall double-pane window assembly in which the outside pane is at 0°C and the inside pane is at 20°C. The panes are spaced 2.5 cm apart. What is the thermal resistance (‘R’ value) of the window if the rate of radiative heat flux is 84 W/m2?
GIVEN • Double-pane window assembly • Height (H) = 1 m • Spacing (?) = 2.5 cm = 0.025 m • Pane temperatures ? Inside (Ti) = 20°C ? Outside (To) = 0°C • Radiative heat flux (qr/A) = 84 W/m2 FIND (a) The rate of convective heat transfer (qc/A) (b) The thermal resistance (R) ASSUMPTIONS • Steady state • Conduction through the window frame is negligible PROPERTIES AND CONSTANTS for dry air at the mean temperature of 10°C Thermal expansion coefficient (?) = 0.00354 1/K Thermal conductivity (k) = 0.0244 W/(m K) Kinematic viscosity (?) = 14.8 × 10–6 m2/s Prandtl number (Pr) = 0.71
The geometry of an ellipse is described by two numbers: the ____ which is half the longest diameter of the ellipse and the ____ which tells us the shape of the ellipse
a. radius, eccentricity b. radius, deferent c. semi major axis, deferent d. semi major axis, epicycle e. semi major axis, eccentricity
A steel lift column in a service station is a solid cylinder 4.0 m long and 0.20 m in diameter. Young's modulus for this steel is 20 × 1010 N/m2. By what distance does the column compress when a 5000-kg truck is on it?
A) 4.7 × 10-7 m B) 8.0 × 10-7 m C) 3.2 × 10-6 m D) 7.8 × 10-6 m E) 3.1 × 10-5 m
Suppose you see two stars: a blue star and a red star. Which of the following can you conclude about the two stars? Assume that no Doppler shifts are involved. (Hint: Think about the laws of thermal radiation.)
A) The red star is more massive than the blue star. B) The blue star is more massive than the red star. C) The blue star is farther away than the red star. D) The blue star has a hotter surface temperature than the red star. E) The red star has a hotter surface temperature than the blue star.