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Mega Friction
gravitational potiential energy?
A 74.4 kg piece of a satellite left over from an explosion with zero orbital velocity in space falls from a distance of 183.18 km above the surface of the earth down toward earth. It arrives with 16.09 MJ (M="mega") kinetic energy on earth. How many MJ energy have been lost due to friction in the earth's atmosphere ? Use the exact expression for the gravitational potential energy.
Gravitational PE = -Gm1m2/r (ref.).
The grav. PE at 183.18 km altitude is -60.75 MJ/kg; at 0 altitude it is -62.495 MJ/kg. The difference is 1.745 MJ/kg or 129.83 MJ total. So the energy loss due to friction is 129.83 - 16.09 = 113.74 MJ.
Using G = 6.6745E-11, r(earth) = 6378160, m(earth) = 5.972E24.
AMF Mega Friction
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powerplant generators?
hi, i would like to ask some questions about generators mechanical energy to electric energy generators such as the ones used in hydro electric dams, steam powerplants, gas turbine power plants and wind turbines. are there different classes of these generators? if so, what are they, and what power out put in mega watts do the create at a given rpm, what is the most efficient rpm ranges of these different generators. how much torque is required to over come the resistance of the friction and weight of the generators to spin at the specific rpm. is there a site i can go to read about the generators not necessarily power plants just the generators? what are the equations people can use to define these stats. i understand im asking alot in 1 question but does anyone know? or does any one know a site or something. please i need help with this information. i need to know all of it, please answer THE questions i asked. thank you
Hydropower generators work at low speed.To keep the frequency match with the grid,They much have more poles.But Steam turbine/gas turbines operates at high speed most 3000RPM for 50 cycles or 3600 rpm for 60 cycles.and are 2 pole .
Large generators are hydrogen cooled density is less so vintage frictions is kept less by hydrogen cooling.
N=120 f/p where N=rpm F=frequency P=number of poles.