You have a cart, track, meterstick, mass set, stopwatch, pulley & table clamp, c

Question

You have a cart, track, meterstick, mass set, stopwatch, pulley & table clamp, cart masses and video equipment. You can change the hanging mass and the cart. A small bolt with a Velcro pad is the friction accessory. It screws into the bottom of the cart.

1. Make a drawing of the problem situation while the cart’s speed is increasing, and another one while the cart’s speed is decreasing. Draw vectors for each drawing to represent all quantities that describe the motions of the block and the cart and the forces acting on them. Assign appropriate symbols to each quantity. If two quantities have the same magnitude, use the same symbol. Choose a coordinate system and draw it.

2. List the "known" (controlled by you)_ and "unknown" (to be measured or calculated) quantities in this problem.

3. Write down what principles of Physics you will use to solve the problem. Will you need any of the principles of kinematics? Write down any assumptions you have made that are necessary to solve the problem and are justified by the physical situation.

4. Start with the time interval in which the string exerts a force on the cart (before object A hits the floor). Draw separate free-body and force diagrams for object A and for the cart after they start accelerating. Check to see if any force pairs are related by Newton’s 3rd Law. For each force diagram (one for the car and one for object A), write down Newton's 2nd law along each axis of the coordinate system. Be sure all signs are correct.

5. Write down an equation, from those you have collected in step 4 above, that relates what you want to know (the frictional force on the cart) to a quantity you either know or can find out (the acceleration of the cart). Is the force the string exerts on the cart equal to, greater than, or less than the gravitational pull on object A? Explain. Solve your equations for the frictional force on the cart in terms of the masses of the cart, the mass of object A, and the acceleration of the cart.

6. Now deal with the time interval in which the string does not exert a force on the cart (after object A hits the floor). Draw a free-body and force diagram for the cart. Write down Newton's 2nd law along each axis of the coordinate system. Be sure your signs are correct. Solve your equation for the frictional force on the cart in terms of the masses of the cart, the mass of object A, and the acceleration of the cart. You can now determine the frictional force on the cart for each case by measuring the acceleration of the cart.

7.Express the frictional force on the cart in terms of quantities that you can measure in the experiment. Make an educated guess about the relationship between the frictional forces in the two situations.

Explanation / Answer

2.

The known quantities are mass of cart, hanging mass, the length of the string and acceleration due to gravity (g).

The unknown quantities are tension in the string, friction, acceleration of the system.

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