A machine is often designed when the work required to move
an object needs a force larger than a person can exert. Your
task is to lift a 400-kg boulder from the ground and place it on
a platform 3.0 m high.
(a) Make a sketch of a machine (or a combination of
machines) that use the force provided by one person to
accomplish this task.
(b) Label the input and output force(s) on your sketch.
(a) Here is a sketch of a machine that could be used to lift the 400-kg boulder:
___________
/
----------- Pulley 1
/
Co･｡.｡･･｡.｡･･｡.｡･･｡.｡･･｡\
| Input force (provided by a person)
|
|
| ________
| /
| ---------------- Pulley 2
| /
________/
Output force (lifting the boulder)
In this sketch, we have two pulleys: Pulley 1 and Pulley 2. The person applies the input force at Pulley 1. The rope is threaded through Pulley 1 and Pulley 2, and the other end is attached to the boulder. As the person pulls down on the rope at Pulley 1, the boulder is lifted up due to the mechanical advantage of the pulleys.
(b) The input force is labeled "Input force (provided by a person)" and is exerted at Pulley 1. The output force is labeled "Output force (lifting the boulder)" and is responsible for lifting the 400-kg boulder.