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course Phy 201
Toy car and magnetsUses toy car, magnets, rubber bands, rulers
Using one magnet to repel the other, which is attached to the cart, propel the cart from magnet separations 8 cm, 5 cm and 3 cm. Measure how far the car coasts for each separation. Sketch a graph of coasting distance vs. separation.
link to graph- http://i1005.photobucket.com/albums/af177/ag1972/coast.jpg
Use your graph to estimate coasting distances corresponding to 4 cm and 6 cm.
Give your data and your estimates:
Car coasts 9cm when separated 8cm.
Car coasts 31cm when separated 5cm.
Car coasts 75cm when separated 3cm.
When separated 6cm the car should coast about 21-22cm.
When separated 4cm the car should coast about 50cm.
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Good. Now assume that the car and magnet have mass 80 grams, and that the coefficient of rolling friction is .03.
What is the force of friction?
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For each trial, how much work is therefore done against friction as the car coasts to rest?
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We can assume that all the potential energy in the magnets, before release, ends up being dissipated against friction after the car is released.
For each trial, how much potential energy do we infer the system has at the instant of release?
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Sketch a graph of PE vs. the separation of the magnets. You will have three points.
Find the average slope between the first and second point, and between the second and third point. Be sure to detail your reasoning of the first slope, including all the quantities used to find the slope, with units at every step.
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What do you think your slopes represent?
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How much potential energy did the magnet system gain between your first separation and your second?
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How far are the magnets displaced between your first separation and your second?
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What therefore is the average magnetic force between these separations?
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Using the same reasoning, find the average magnetic force between the second and third separation.
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At what point after its release do you think the car reached its maximum velocity? What could you easily measure to obtain a reasonable prediction of the point at which this should occur?
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