060218_notes10questions

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20:00:26 Why does it make sense that the work done by gravity on a set of identical hanging washers should be proportional to the product of the number of washers and the distance through which they fall?

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RESPONSE --> gravity is acting on them the whole time they are there. So the more washers that are there the more gravity is being exercted on them.

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20:00:30 ** When force is parallel to displacement, work is force * distance, so the proportionality with distance follows immediately. The force comes from the gravitational interaction of the masses of the washers with the Earth's gravitational field. More washers imply more force, and the force is proportional to the number of washers. **

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RESPONSE --> ok

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20:04:19 Why is this consistent with the idea that the work done on a given cart on an incline is proportional to the vertical distance through which the cart is raised?

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RESPONSE --> Th steep the incline the more it takes to pull the cart. The number of washers is proportional to the incline.

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20:04:23 ** The steeper the incline the more washers are required to pull the cart up the incline. In fact for small inclines and correcting for friction the number of washer is proportional to the slope of the incline. The vertical distance, being the rise through which the cart is raised, is also proportional to the slope of the incline. So for a given cart the number of washers is proportional to the incline. Since work is proportional to the number of washers we conclude the work is proportional to the vertical distance through which the cart is raised. **

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RESPONSE --> ok

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20:06:43 How does the work done against friction of the cart-incline-pulley-washer system compare with the work done by gravity on the washers and the work done to raise the cart?

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RESPONSE --> The work done by friction and the work done to get the cart up the incline are all part of gravitional force acting on the weight.

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20:06:47 ** The work against friction plus the work done to raise the cart are all provided by the gravitational force acting on the descending weight. **

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RESPONSE --> ok

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20:08:58 How do we establish, using a cart-pulley-washer system on a constant-velocity incline, that the acceleration of cart is proportional to the net force on the cart?

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RESPONSE --> The larger the slope the more gravity has its effects on it. The larger the slope the more force that is needed pull the cart up.

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20:10:04 ** STUDENT ANSWER: In order to keep the velocity constant the amount of force should be constant but it must overcome the effects of gravity and therefore it must increase at a constant rate . The increase in the ramp slope will correspond to the increase in the force. INSTRUCTOR RESPONSE: Good start. This is half of it. This indicates how the force on the cart is proportional to acceleration. The other half is that the acceleration of the cart is proportional to the effective slope. Since the force and the acceleration of the cart are both proportional to the effective slope, they are proportional to each other. **

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RESPONSE --> Also the slope and the acceleration are proporitonal

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Good. Let me know if you have questions.