Physics 207 GH Exam 2 Supplement

Dr. Min Xu

Apr 9, 2003
LAST NAME: ___________________________________________________________________________________________________ FIRST NAME: __________________________________________________________________________________________________ SS#: ________________________________________________________________________________________________________________

General Instruction

You have 1 hour to answer 2 questions on this exam. Work each problem only on the sheet provided for this problem, using the back if necessary. Please write the name and the last four digits of your SS# on each sheet at the top of the page.

You must indicate the reasoning and show all the steps.

If you are unable to obtain the answer to part of a problem and you need the answer to solve the subsequent parts, use an appropriate symbol for the answer to the previous part and solve in terms of that symbol.

1. (20 points) The rope and pulley have negligible mass, and the pulley is frictionless. Initially the 6.00-kg block is moving downward and the 8.00-kg block is moving to the right, both with a speed of 1m/s. The blocks come to rest after moving 2.00m. Use the work-energy theorem to calculate the coefficient of kinetic friction between the 8.00-kg block and the table top.

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2. (30 points) A small rock with mass m is fastened to a massless string with length l to form a pendulum. The pendulum is swinging so as to make a maximum angle of h0 with the vertical. Air resistance is negligible.


(a) (10 points) What is the speed of the rock when the string passes through the vertical position?
(b) (10 points) What is the tension in the string when the string makes an angle of h0 with the vertical?
(c) (10 points) What is the tension in the string as it passes through the vertical?

3. (30 points) A movie stuntman (mass 80kg) stands on a window ledge 5m above the floor. Grabbing a rope attached to a chandelier, he swings down to a grapple with the movie’s villain (mass 70kg), who is standing directly under the chandelier. Assume that the stuntman’s center of mass moves downward 5.0m before he releases the rope as he reaches the villain.


(a) (10 points) What is the speed of the stuntman as he reaches the villain.
(b) (10 points) With what speed do the entwined foes start to slide across the floor?
(c) (10 points) If the coefficient of kinetic friction of their bodies with the floor is 0.250, how far do they slide?
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