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Learning Introductory Physics with Activities

Paul J. Emigh, Rebecka Tumblin, Kathryn Hadley, Danielle Skinner

Section 4.7 Applications of Friction

Subsubsection Practice Activities

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Activity 4.7.1. The Crate on Top of the Truck.

A truck is initially moving to the right with speed \(v_i\text{.}\)
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Figure 4.7.1. A crate on top of a truck.
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(a)

What force causes the crate to accelerate?
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(c)

What do you think would happen in the above example if the coefficients of friction were very big? Very small?
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(d)

Suppose the driver suddenly has to slam on the brakes, causing the crate to begin sliding. What is the crate’s acceleration? Which things are different compared to the first example?
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Activity 4.7.2. The Book against the Wall.

You push a book against a vertical wall so the book does not move.
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(a)

Use Force Analysis to understand the magnitudes of the forces acting on the book. What happens to each force if you push harder?
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(b)

Suppose you push a different book horizontally against a vertical wall so that the book slides downward at constant speed. You know the coefficients of friction are \(\mu_b\) (between the book and the wall) and zero (between the book and your hand). You also know the mass \(m\) of the book. Use Force Analysis to find the magnitude of the force your hand must exert on the book.
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A*R*C*S 4.7.3. Suitcase on a Ramp.

A suitcase of mass \(m\) is at rest on a ramp that makes an angle \(\theta\) with the horizontal. You know the coefficients of friction (\(\mu_s\) and \(\mu_k\)) between the suitcase and the ramp. Determine the possible angles for which the suitcase remains at rest.
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Hint.
Remember to follow the A*R*C*S Steps.
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