How to find the coefficient of Friction?

AI Thread Summary
To find the coefficient of friction for a 15 kg cardboard box sliding 7.0 m and stopping in 3.3 s, the deceleration must first be calculated using kinematic equations. The forces acting on the box include gravity, normal force, and friction, which can be analyzed through a free-body diagram. The average speed and initial speed can be determined from the distance and time, allowing for the calculation of deceleration. Once deceleration is known, it can be used alongside the forces to find the coefficient of friction. Understanding these relationships is crucial for solving the problem effectively.
luxford
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Homework Statement



A small 15 kg cardboard box is thrown across a level floor. It slides a distance of 7.0 m, stopping in 3.3 s. What is the coefficient of friction between the box and the floor?

Homework Equations





The Attempt at a Solution



I didn't know how to do it. I just drew a free-body diagram of it. :|
 
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What forces do you have in your FBD? What is the deceleration (a) according to your forces equation and (b) according to the given data?
 
The forces I have on my FBD is the force of gravity, normal force, and force of friction.

As for deceleration, it is not given...
 
luxford said:
The forces I have on my FBD is the force of gravity, normal force, and force of friction.

As for deceleration, it is not given...
You know the equation ƩF=ma, right? Apply this in the horizontal and vertical directions to obtain two equations.
 
luxford said:

Homework Statement



A small 15 kg cardboard box is thrown across a level floor. It slides a distance of 7.0 m, stopping in 3.3 s. What is the coefficient of friction between the box and the floor?

Homework Equations





The Attempt at a Solution



I didn't know how to do it. I just drew a free-body diagram of it. :|

What's the average speed? So then what's the initial speed?
Then, can we equate initial k.e. with friction energy loss to compute the friction coefficient?
 
luxford said:
The forces I have on my FBD is the force of gravity, normal force, and force of friction.

As for deceleration, it is not given...

If you have t, d, and vf, you can find the deceleration using kinematics.

Since you have all three of these, finding deceleration is quite simple.

d=vft+\frac{1}{2}at2
 
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