work and power
in everyday life work has many different meanings, but to scientists it is something very precise.
work is done when a force causes an object to move or prevents it from moving. The amount of work done can be calculated using the following equation:
work done = force *distance moved in the direction of the force
the above equation can be explained in words. that is to say , work done equals force times (or multiplied by) distance moved in the direction of the force.
if a force of 1 n (newton) causes an object to move 1 meter, then 1 j (joule) of work has been done.
for example, in order to raise the weights above his head, this athlete must apply a force of 2000 newtons, which causes them to move up to the height of 2 meters. in doing so he is doing work.
then , the work done by the athlete is : the force applied by him times the distance moved. if can be calculated in this way:
work done=2000n*2m=4000j
so, the answer is 4000 joules.
in another example, in order to cut the lawn, this lady must push her lawnmower. a force, 80 newthons, is needed to make the lawnmower move. There is a force , 50 newtons, from the engine acting to push the lawnmower forward. the lady has to apply more so that the lawnmower can move along a straight line for a distance of 40 meters. as she does so, she is doing work.
first, we should work out the force which the lady applies to make the lawnmower move on. since the force needed to move the lawnmower is 80 n and the engine has a force of 50 n , the lady's force can be obtained by doing the following calculation:80 n-50n =30n.it can be explained in words:80 newtons minus 50 newtons equals 30 newtons. so, the force applied by the lady is 30n.
then we can calculate the work done by the lady:
work done =30n *40j =1200j
thus, the work done by the lady is 1200 joules.
power is a measure of how rapidly work is being done. it is measured in watts(w). if a person or a machine is doing 1j of work each second, the power rating is 1 w (watt).
power=(work done)/(time taken)
the equaltin can be explained in words:power equals work done divided by time taken.
now, let's look at the athlete. what is the power of the athlete? if it takes the athlete 0.5 second to lift the weights obove his head, the power of the althlete above is:
power=(4000j/0.5s)=80000w or 8kw
thus, the answer is 8000w or 8kw
now , can you tell the power of the lady above if she uses 200 seconds to finish cutting the lawn for a distance of 40 meters?