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Unformatted text preview: Name: Physics 121, Dr. Callahan Summer I 2008, Midterm #2 Note: Show your work. Clarity counts. 1 2 3 4 1. An amusement park ride consists of a cylindrical room of radius R . You stand by the wall, the room starts spinning, the floor drops and you stick to the wall by friction. If you are moving with speed v , what minimum co¨ efficient of static friction μ s must there be between you and the wall? Answer: There are three forces acting on you: your weight mg down, a normal force N horizon- tally, and a friction force F f up. The acceleration is v 2 /R horizontally. Thus the horizontal component of Newton’s second law is N = mv 2 R . The vertical component is F f- mg = 0 ⇒ F f = mg. We also know that F f ≤ μ s N , so mg = F f ≤ μ s N = μ s mv 2 R ⇒ μ s ≥ Rg v 2 . 2. Two masses are suspended from massless pulleys as shown below. Solve for the tension in the rope. m 1 m 2 Answer: Let down be the positive direction for both. Then Newton’s second law for the first mass is...
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This note was uploaded on 07/12/2008 for the course PHY 121 taught by Professor Chamberlin during the Summer '08 term at ASU.
- Summer '08