00:01
And this problem wears to find how far a hockey puck is going to slide, even that it has a kinetic friction coefficient with the ground on which it's sliding of 0 .05.
00:15
We're told that the puck has an initial velocity or initial speed of 5 meters per second, and we want to let it roll all the way until it's stuffed.
00:25
So its final velocity or final speed is going to be 0 meters per seconds.
00:29
Additionally, there is no change in height, so we can conveniently set the gravitational potential to be at the reference value, which we can set to be zero.
00:41
So we can set the height to be at zero meters, which then since potential energy is given by mass times the irritation acceleration times the height, if y is zero, this is always going to be zero for this particular problem.
00:56
And the last piece of the puzzle that we need is what is the energy going to transform into? so the energy is going to transform into the work done by friction in stopping or absorbing essentially the kinetic energy that the puck has.
01:16
So if you think about the free -body diagram of the puck, this is what it looks like.
01:21
So it has a mass, so it's got some weight.
01:26
And it's not moving in a vertical direction.
01:28
There's a normal force on it, which is equivalent to the weight, in magnitude at least.
01:34
And associated with that normal force, there's going to be a kinetic friction force.
01:40
So the friction force is equal to the kinetic friction coefficient, so mu k times n, where n is the vector, is the normal vector.
01:53
And so the normal vector, since it's equal, it is equal to the weight is going to be mass times g.
02:00
So summing it all up, the magnitude of the kinetic friction force is going to be mu k times m g.
02:08
And the work done by this force is the dot product of this force with the displacement vector...