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E X P E R I M E N T
11
Experimental Planning
A common experimental setup is shown in GL Fig. 11.1 for a car moving up an inclined plane at a constant speed pulled by a
descending mass suspended over a pulley. Free-body diagrams for the forces acting on each object are also shown.
1. Write an equation for the sum of the forces acting on the car parallel to the plane and also for the sum of the forces acting
on the descending mass. Note that the car and descending mass both move with constant velocities.
2. If the mass of the connecting string is small compared to the other masses, F and T will be approximately equal. Use this
result to combine the equations and solve for the force of friction f in terms of the masses and angle.
Did your result include a sin u term? Check with a classmate or the instructor to verify your result.
3. Now consider the case of the car moving down the plane with a constant speed, pulling a smaller mass upward. Draw the
free-body diagrams and repeat the process used above to obtain an expression for f in this case. (Use m2 for the ascending
mass.) How does this result compare to the previous one?
Note that Wf 5 f d applies in both cases of the block moving up and down the plane, where d is the distance the block
moves.
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