Newton's Laws Legacy Problem #25 Guided Solution

This is a difficult problem that will require a solid understanding of physics, effective problem-solving habits, and some good thinking. What we read about is a hockey puck that is moving across the ice and slowing down from 10.5 meters per second to 8.8 meters per second in 14 seconds. These three pieces of information have nothing to do with F net equal ma directly. You should recognize that these are speed values and time values. And from our understanding of acceleration, we should be able to use these quantities to calculate the value of the acceleration, a equal delta v over t. So as I look at these numbers, what I'm thinking about is, I can calculate the acceleration. Now that's the first part of the question, find the acceleration, so let's just do that right now. The final value minus the initial value divided by the time is the acceleration, comes out to be a negative value, meaning that the object is slowing down as it moves in the forward direction. Now once you get that acceleration, now you have to think some more. You have to think about finding the force of friction and the coefficient of friction. Now if I think about finding the force of friction, and there's two ways to do it, you could go mu times F norm, if you knew mu, but obviously you don't because they're asking you to find that. So you have to approach that friction force from another viewpoint. You can find the friction force if you start to construct a free body diagram on this puck sliding to the right and slowing down. To the right part is something I'm assuming. So draw a picture of a puck, pretend it's moving to the right, and begin to draw the forces acting up on it. Now you have to think, and you have to use your physics understanding. Like any object, the puck will experience a down force, a force of gravity. So draw an arrow down, label it F grav. It also experiences an up force, a support force from the ice pushing up on it. That's called F norm. So draw an arrow up, label it F norm. Since the puck is accelerating leftward as it moves to the right, the ups and down forces are going to be balancing each other. So what you know is that the F norm equals the F grav. So you could calculate F grav, it's just mg, 0.162, times the value of g, 9.8, and you get the down force, and you also get the up force. There's one more force, though, and that's the force of friction. It's off to the left, and that force of friction is the unbalanced force acting on the object. It's equal to ma. So take the mass, 0.162, and multiply by the acceleration value, and you get your net force, and you also get your friction force. Now to calculate the coefficient of friction, use an equation, F frict equals mu F norm. The normal force is equal to the gravity force, the friction force you've just solved for. So substitute those values into the equation, and solve for mu, the coefficient of friction.