3.The rope alone.Sincethe weightof the rope is N/m and the heightis meters,the total weightof
the rope from the floor to a heightof metersis
But sincethe workeris constantlypullingthe rope,the rope’s lengthis decreasingat a constantrate and
thus its weightis also decreasingas the bucketbeinglifted.So at meters,the metersthere
remainto be liftedof weight N. Thusthe workdoneto lift the weightof the rope is
4.The bucket,the sand,and the rope together. Herewe are askedto sum all the workdoneon the empty
bucket,the sand,and the rope.Thus
FluidStatics:Pressure
You haveprobablystudiedthatpressure is definedas the forceper area
whichhas the unitsof Pascals or Newtonsper metersquared, In the studyof fluids,
suchas waterpressureon a dam or waterpressurein the oceanat a depth anotherequivalentformula
can be used.It is calledthe liquidpressure at depth :
where is theweightdensity, whichis the weightof the columnof waterper unit volume.For example,if
you are divingin a pool,the pressureof the wateron your bodycan be measuredby calculatingthe total
weightthat the columnof wateris exertingon you timesyour depth.Anotherway to expressthis formula,
the weightdensity is definedas