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hw 22 sol

# hw 22 sol - Patel(pnp223 homework 22 Turner(92160 This...

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Patel (pnp223) – homework 22 – Turner – (92160) 1 This print-out should have 12 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Two pucks are attached by a stretched spring and are initially held at rest on a frictionless surface, as shown. The pucks are then released simultaneously. I II If puck I has three times the mass of puck II, which of the following quantities is the same for both pucks as the spring pulls the two pucks toward each other? 1. Acceleration 2. The magnitude of the momentum cor- rect 3. Speed 4. Kinetic energy 5. Velocity Explanation: The total momentum is conserved here (no friction). 0 = vectorp i = vectorp f = vectorp I + vectorp II vectorp I = vectorp II bardbl vectorp I bardbl = bardbl vectorp II bardbl The magnitude of momentum is the same for both pucks. Let’s look at the other choices: ( m I = 3 m II ) Speed: m I v I = p I = p II = m II v II = v II = 3 v I . Velocity: m I vectorv I = vectorp I = vectorp II = m II vectorv II = vectorv II = 3 vectorv I . Acceleration: vectora I = vector F I m I = vector F II 3 m II = 1 3 vector F II m II = 1 3 vectora II . Kinetic energy: K I = 1 2 m I v 2 I = 1 2 (3 m II ) parenleftbigg 1 3 v II parenrightbigg 2 = 1 3 parenleftbigg 1 2 m II v 2 II parenrightbigg = 1 3 K II . 002 (part 1 of 3) 10.0 points Given: Two masses ( M 1 and M 2 ) are a sys- tem. Let E = K + U be the total mechanical energy of the system and vectorp be the total mo- mentum of this system. A mass m 1 slides on a frictionless horizontal plane and collides and sticks to a mass m 2 that is at the bottom of a frictionless ramp. m 1 m 2 v 1 What is conserved in the collision? 1. E is conserved in the collision. 2. Both E and vectorp are conserved in the colli- sion. 3. Neither E nor vectorp is conserved in the colli- sion. 4. vectorp is conserved in the collision. correct Explanation: This is an inelastic collision (the two masses stick together) so mechanical energy E is not conserved. There is no net external force act- ing on the system during the collision (the force due to gravity acting downward is can- celled by the normal force acting upward), so momentum vectorp is conserved.

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