You anchor the rope at one end and arrange a moveable pulley to achieve a mechanical advantage of 2. By the time you have lifted the object 5m off the ground, how much rope have you pulled through the pulley?
(a) 2m
(b) 5m
(c) 7m
(d) 10m
4 Answers
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You can achieve a 2:1 advantage with a single pulley by rigging the pulley to the load. This is usually not practical for lifting but can be used for pulling a load horizontally quite easily. Say you need to pull a vehicle out of a ditch. Attach a strong rope to a tree then feed it through a pulley attached to the stuck vehicle and then to a pulling vehicle. For every two meters the pulling vehicle moves, the other vehicle will move one meter thus doubling the pulling force.
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Mechanical advantage is a ratio of output to input.
A mechanical advantage of 2 implies that twice
the output has been achieved for the input.
Pulling 10 meters of rope and gaining 5 meters
of lift means that the object will appear to have
half as much weight. Essentially, you have pulled
twice as much rope, but half as heavy for each tug.
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How do you rig a single pulley to give a mech advantage of 2?
Edit: Thanks Gnarlok for helping me remember my elementary school science, memory of which was apparently on vacation when I answered this one.
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d) 10 metres.
but you knew that…………..
