Engineering belt drive question..find the force on the tight side?

Posted on 2014-04-04 08:09:00 in Engineering by S

Not your typical belt drive question which is why I am unsure how to start it...:



On piers to bring small and medium sized boats to stop a device is used. It consists of two cast iron posts (bollards) built in a concrete foundation. When a boat approaches the pier a sailor throughs a rope and another sailor puts several loops around the bollards in “S” pattern (see figure below). Then he puts a free end of the rope on the pier and fixes it with his foot applying his body weight. The frictional force of the rope with the concrete pier creates a force Fs at the slack end of the rope. At the opposite end (tight end) a force Ft is developed that brings the boat to stop. Assuming that the sailor’s body weight is 1000N, frictional coefficient of the rope with concrete is fc = 0.25, and the frictional coefficient of the rope with bollards is fp = 0.2, determine what stopping force Ft will be developed for one loop, two loops, three loops, four loops, five loops and six loops. Use dimensions shown in figure below.



so we know the belt does not run on either side of the pulleys, it crosses and makes an s-shape.

slack end on bottom, tight on top

free end is held down with 1000N at slack end where friction coefficient for concrete pier is 0.25. Force on slack end is Fs

Force on tight end is Ft<trying to find this

friction coefficient of rope with bollards (tight end) = 0.2



now how would I change any values to take into account the # of loops? Multiply the frictional coefficients...

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