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Unformatted text preview: johnson (mjj622) – HW 13 – Coker – (56625) 1 This print-out should have 16 questions. Multiple-choice 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
- Static Equilibrium