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Unformatted text preview: ile quake.
4. Why not red-line it? The image at right shows one cylinder in a 4-stroke internal
combustion engine. The piston P is connected to the
crankshaft C via the connecting rod R. A common
engine failure mode is to break a connecting rod.
(a) Assume that the piston undergoes simple harmonic
motion with a top-to-bottom displacement of 10 cm.
What is the maximum engine speed (in rpm) such
that the tension in the connecting rod remains less
than the ultimate strength of the steel from which it
Assume that the piston has mass
m=0.5kg, that the connecting rod is cylindrical with a
diameter of 3 cm, and that the ultimate strength F/A
of steel is 500 MPa. Neglect the mass of the
connecting rod and any forces exerted by the gases
within the cylinder
(b) At what engine rpm will the connecting rod tension
Physics 2214, Spring 2011 2 Cornell University be half the value in (a)?
(In fact, due to drag forces on the cylinder as it moves up and down, the tension in the
connecting rod increases as the cube of the engine speed, not as the square, so that
failure will occur at a smaller rpm than you've calc...
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