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Unformatted text preview: t: what is the total kinetic energy at that instant? Make
3. Why use electrons? Why not transmit power down power lines mechanically instead
of electrically? Let's assume you send transverse waves down a 2 cm diameter
power line that is made of an aluminum alloy with density 2700 kg/m3 and an
ultimate strength (beyond which it fails) of 400 MPa. Neglect the line's weight, and
assume that it is under a uniform tension corresponding to 1/10 its ultimate strength.
We drive one end of the power line up and down at 60 Hz, launching a harmonic
traveling wave of amplitude A. What must be the amplitude A for the average power
transmitted by the wave to be (a) 1 MW and (b) 400 MW (more typical of large
diameter, 765 kV power lines)? What would be the maximum transverse speed of
the power line in (b)? (People who live near power lines tend to worry about possible
ill effects. Would mechanical power transmission be likely to decrease or increase
4. Energy and Power in Sound Waves. Let'...
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