00:01
You are lowering two boxes, one on top of the other, down a ramp by pulling a rope parallel to the surface of the ramp.
00:07
Both boxes move together at a constant speed of 15 centimeters per second.
00:12
The coefficient of kinetic friction between the ramp and the lower box is...
00:17
So if the u .k.
00:21
Is 0 .444.
00:23
And the coefficient of static friction is 0 .800.
00:31
What force do you need to exert to accomplish this? okay, so let's start with a free body diagram.
00:40
So here's our ramp.
00:44
This is 90 degrees.
00:47
This is theta.
00:49
And our boxes are sitting on top of each other.
00:52
We have a normal force that comes out perpendicular to the surface.
00:58
This is static friction while the bottom one is kinetic friction.
01:04
The bottom one is moving and the top box is kind of staying in place.
01:10
So static versus kinetic.
01:13
And then dealing with the weights, you're going to have, let's call positive y, positive x.
01:25
So you're going to have a weight that pulls down at m1.
01:29
Plus m2g and then by geometry cosine of theta.
01:37
This is m2g sine of theta, and this is m1g sine of theta...