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Unformatted text preview: johnson (mjj622) – HW 13 – Coker – (56625) 1 This printout should have 16 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. This assignment deals with the static equi librium portion of Ch. 14, which will be the last material included on Quiz 3, November 10. 001 (part 1 of 2) 10.0 points Consider an extended object (not a point), with forces vector F acting on it, producing torques vector τ . Is it possible for a situation to exist in which the net force acting on the object (the net force is the sum of all the individual forces act ing on the object) is equal to zero parenleftBig summationdisplay vector F = 0 parenrightBig while the net torque about any axis (the net torque is the sum of all the torques acting on the object) is not equal to zero parenleftBig summationdisplay vector τ negationslash = 0 parenrightBig ? 1. Yes. correct 2. No. Explanation: Yes — if the forces are equal and opposite, but do not act along a common line, like pulling the top of a box while pushing the bottom (on the same side), the net force is zero, while the net torque is not! 002 (part 2 of 2) 10.0 points Is it possible for a situation to exist in which the net torque acting on the object is zero parenleftBig summationdisplay vector τ = 0 parenrightBig while the net force acting on the object is not equal to zero parenleftBig summationdisplay vector F negationslash = 0 parenrightBig ? 1. No. 2. Yes. correct Explanation: Yes again — for example, just one force acting on the center of mass of an object produces no torque, but certainly produces a net force! 003 (part 1 of 3) 10.0 points A solid sphere of radius R and mass M is held against a wall by a string being pulled at an angle θ . f is the magnitude of the frictional force and W = M g . W P F θ R To what does the torque equation summationdisplay i vector τ i = 0 about point O (the center of the sphere) lead? 1. F cos 2 θ = f 2. F sin θ = f 3. F = f correct 4. W = f 5. F sin θ cos θ = f 6. F + W = f Explanation: W P F θ R R f Applying rotational equilibrium about O , the center of the sphere, summationdisplay i vector τ i = 0, so τ CW = τ CCW F R = f R johnson (mjj622) – HW 13 – Coker – (56625) 2 F = f . 004 (part 2 of 3) 10.0 points To what does the vertical component of the force equation lead? 1. F sin θ = W 2. F sin θ = f + W 3. F sin θ = f 4. F cos θ + W = f 5. F sin θ + f = W correct Explanation: Applying translational equilibrium verti cally, summationdisplay i F yi = F sin θ + f −W = 0 F sin θ + f = W . 005 (part 3 of 3) 10.0 points Find the smallest coefficient of friction μ needed for the wall to keep the sphere from slipping....
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This note was uploaded on 02/10/2011 for the course PHY 303K taught by Professor Turner during the Fall '08 term at University of Texas.
 Fall '08
 Turner
 Static Equilibrium

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