00:01
We want to calculate the normal force on this 17 .7 kilogram block.
00:06
The first situation is the block sitting on a level surface.
00:14
The strategy with these problems is to draw a picture, assign a coordinate system, draw the forces, and then apply some of the forces equals ma.
00:35
Okay, we're going to do this in the y direction, so up and down, so plus y.
00:41
In the plus y we have normal force.
00:44
In the negative y we have mg.
00:47
And it is not accelerating.
00:48
So that's equal to zero.
00:51
So our normal force is equal to the weight of the block.
00:58
173 .46 newtons.
01:03
Okay, next the block is on a surface tilted up at 25 .8 degrees.
01:22
Okay, so tilt it up at this angle.
01:25
What's the normal force? well, for blocks on tilted surfaces, you want to change your coordinates so that the x direction is parallel to the surface and the y direction is perpendicular.
01:42
Then we want to come over here and draw our free body diagram again, or draw, we haven't drawn it before, draw our free body diagram.
01:56
We have the normal force and gravity, but the normal, or the gravitational force, is in both the x and the y direction.
02:07
So we need to assign an angle.
02:11
That angle is that angle they give us, theta, that top angle, so that we can break down our gravitational force into x and y components.
02:23
So some of the forces in the y equals zero.
02:27
It's not accelerating.
02:29
The normal force minus m g cosine theta.
02:34
Mg cosine theta gives you the y component of that gravitational force equals zero.
02:43
So the normal force is equal to mg cosine theta 156 .169 newtons...