What class of asteroids is a threat to Earth and other terrestrial planets? Why?
What will be an ideal response?
Earthgrazers have perihelions inside the Earth's orbit, and thus could potentially hit the Earth, crossing our own orbit, as well as those of Mars, Venus, and even Mercury.
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An 20 cm-diameter horizontal steam pipe carries 1.66 kg/min of dry saturated steam at 120°C. If ambient air temperature is 20°C, determine the rate of condensate flow at the end of 3 m of pipe. Use an emissivity of 0.85 for the pipe surface. If heat losses are to be kept below 1 per cent of the rate of energy transport by the steam, what thickness of fiberglass insulation is required? The rate of energy transport by the steam is the heat of condensation of the steam flow. The heat of vaporization of the steam is 2210 kJ/kg.
GIVEN • A horizontal steam pipe in air • Pipe outside diameter (D) = 20 cm= 0.2 m • Mass flow rate of steam (ms) = 1.66 kg/min=0.0277 kg/s • Steam temperature (Ts) = 120°C =393 K • Ambient air temperature (T?) = 20°C= 293 K • Emissivity of pipe surface (?) = 0.85 • Heat of vaporization (hfg) = 2210 kJ/kg FIND (a) Rate of condensate flow (mc) at the end of 3 m of pipe. (b) Thickness of fiberglass insulation (S) to keep loss below 1% of the energy transport by steam ASSUMPTIONS • Steady state • Air is still • Thermal resistance of the convection in the pipe and of the pipe wall are negligible • The surroundings behave as an enclosure at T? • Insulation is foil covered, its emissivity ? 0.0 PROPERTIES AND CONSTANTS the Stephan-Boltzmann constant (?) = 5.67 × 10–8 W/(m2 K4) Thermal conductivity of fiberglass (ki) = 0.035 W/(m K) for dry air at the mean temperature of 70°C Thermal expansion coefficient (?) = 0.00291 1/K Thermal conductivity (k) = 0.0288 W/(m K) Kinematic viscosity (?) = 17.1*10-6 m2/s Prandtl number (Pr) = 0.71
What observational evidence suggests that the centers of quasars are small, about a fraction of a light-year?
A. photographs of quasars B. the fact that quasars are so distant, and therefore are very young C. They emit radiation over a very wide range of wavelengths D. The intensity of their radiation fluctuates over periods of months E. All of these choices are correct.
A styrofoam container used as a picnic cooler contains a block of ice at 0°C. If 225 grams of ice melts in 1 hour, how much heat energy per second is passing through the walls of the container? (The heat of fusion of ice is 3.33 × 105 J/kg).
What will be an ideal response?
The change in momentum of an object is equal to the
A) force acting on it. B) change in its velocity. C) object's mass times the force acting on it. D) impulse that acts on it. E) all of the above