# Physics

a screw jack whose pitch is 3mm is used to lift a load of 400kg through a length of 14cm,the length bar of jack is 20cm.if the efficiency of the jack is 60% . calculate
a.velocity ratio of the jack
c.effort required to lift the load
d.workdone by the effort?

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1. every turn your hand moves around circle with radius 0.20 meters

2 pi r = 1.23 meters
that raised the load 0.003 meters
ratio = 1.23 / 0.003 = 409
that is also the mechanical advantage if efficiency is perfect 100%
but in reality .6 * 409 = 245
400 kg * 9.8 = 3920 Newtons up on load
your hand pushes with 3920 /245 = 16 Newtons hand push
work done on load = 400*9.8 * 0.14 Joules
so work done by hand = 400 * 9.8 * 0.14 / .6 Joules

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Damon

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