00:01
So what we've got is there's a ramp up to a height h.
00:07
And we start our block at the top of the ramp, and it's got mass equals 2 .25 kilograms.
00:14
And it slides down, and then at the bottom of the ramp, there's a rough patch of distance d rough equals 15 .0 .10 centimeters or 0 .15 meters.
00:29
Now, we want to find the block speed v after it's crossed the patch.
00:36
In fact, we know that this speed is 4 meters per second, so we want to find the h that's going to cause that.
00:44
So what we're going to do is, first of all, let's look at the energy that the block gains because it's gone down this ramp.
00:52
So delta kinetic energy because of the ramp is going to be minus the change in potential energy on the ramp, which is minus mg delta h.
01:12
But delta h is minus h.
01:14
So this is mghh.
01:17
But now when it's passing over the rough patch, let's draw a free body diagram.
01:23
It's going at a speed, you know, it doesn't matter what its speed is.
01:26
The point is that it's got mg acting downwards, causing there to be a normal force of mg, which means that there's a friction force which opposes its motion of mumg...