AP Physics 1 : Force of Friction
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Example Questions
Example Question #131 : Forces
A box is shoved and is sliding on a concrete floor. It has a mass of 
None of these
Work is due to friction:
Solving for
Plugging in values:
Example Question #740 : Ap Physics 1
A 
Because the block is traveling on an inclined ramp and experiences friction, the two main forces at work here are a component of gravitational force and kinetic frictional force.
The total force acting on the block can be written as 
We know that forces can be expressed as 
The component of gravity parallel to the ramp is given by 
Our total force can hence be expressed as 
Thus,
and
Example Question #31 : Force Of Friction
Jennifer has a mass of 
Solving for the coefficient of friction:
Example Question #32 : Force Of Friction
Consider the following scenario:
A sledder of mass 
The hill has a height of 
We can use the expression for conservation of energy to solve this problem:
The problem statement tells us that the sledder is initially at rest, so we can eliminate initial kinetic energy. Also, if we assume that the bottom of the hill has a height of 0, we can eliminate final potential energy to get:
From here we need to determine what is going to contribute to work. The only extra piece of information we have in this problem is that there is an average frictional force. Therefore that will be the only source of work. Let's began expanding each term, going from left to right:
Note that we didn't mark the height as an initial height because we assumed that the bottom of the hill has a height of 0.
Where d is the length of the hill. We can calculate this distance using the height and angle of the hill.
Rearranging for distance:
Substituting this back into our expression for work, we get:
Now our final term:
Now substituting expression 2, 3, and 4 into expression 1, we get:
The reason we are subtracting friction is because it is removing energy from the system. Another way we could have written our initial expression would be to have work on the final state and then friction would be positive.
Rearranging for the frictional force:
We have all of these values, so time to plug and chug:
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