00:01
In this problem, we're going to talk about power.
00:03
So we need to remember that the power is defined as the energy per unit of time, transferred to a system or exerted by a system.
00:15
And particularly, i'm interested in writing this power when a constant force, f, acts on a system, and causes the system to move with a constant velocity v.
00:39
Now, this may seem counterintuitive because a force is being applied on a system and the system is moving with constant speed.
00:49
But notice that if, let's say there is a force f to the left and a force, let's say f prime to the right, and let's say that they cancel each other out, such that they are equal in magnitude, then the object can move with a constant speed and still have two forces acting on it.
01:15
And let's say we want to know what is the power exerted by force f.
01:21
Then the power is equal to f times v.
01:28
And there is an intuitive way of thinking about this.
01:32
Remember that f times delta x is the work done on the object and we have to divide it by delta t so this is f v so this is the equation we are interested in and in our problem we have three workers each is exerting a power of 165 watts over a system of pulleys and the system of pulleys has an efficiency of 0 .7 that is 75%, meaning that this is the, for each joules of energy that the workers put on the system, the pull is only transferred 0 .75 joules to whatever is being carried by the system of pulleys...