00:01
Okay, so in this problem, we have five shelves, and the first one is 10 centimeters above the floor.
00:11
And the second one is an additional 30 centimeters above the floor, and we have four more, or three more.
00:23
So one, two, three, four, five.
00:27
This is not to scale.
00:29
So this here is ten, ten.
00:32
Centimeters.
00:34
We want that in meter, so we'll put 0 .1 meter.
00:40
This next one is an additional 30 centimeters, so that's 0 .4 meters.
00:55
Next one up is 0 .7 meters, so 30 more than, or 0 .3 more than point four.
01:06
The next one will be one meter and the last one is a height of 1 .3 meters.
01:25
So these are the heights of the different shelves and we want to know the work it takes to put about 25 books per shelf.
01:33
So the information that they give us is that the mass of each book is about 1 .5 kilograms.
01:40
We have about 25 books per shelf and also that each book is about 21 centimeters long.
01:53
So the length of each book is 21 centimeters or 0 .21 meters.
02:06
So work is going to be given by, so in general it's given by the mass times g times the height that we're lifting it up.
02:17
We have 25 books per shelf, so that's going to be 25 times what it takes to lift it to each individual shelf for each one.
02:27
But we also have to consider that the book is 21 centimeters long, and we're not technically lifting it up just to the bottom of that shelf...