HW06-solutions

# HW06-solutions - burgin(lcb626 HW06 markert(56480 This...

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burgin (lcb626) – HW06 – markert – (56480) 1 This print-out should have 22 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 10.0 points A rock of mass m is thrown horizontally off a building from a height h . The speed of the rock as it leaves the thrower’s hand at the edge of the building is v 0 as shown. v 0 h Δ x How much time does it take the rock to travel from the edge of the building to the ground? 1. t = radicalbig hv 0 2. t = hv 0 g 3. t = radicalBigg 2 h g correct 4. t = h v 0 5. t = 2 h g Explanation: The motion of the rock in the y -direction is a free falling motion from rest: h = 1 2 gt 2 t = radicalBigg 2 h g . 002 (part 2 of 2) 10.0 points What is the kinetic energy of the rock just before it hits the ground? 1. K f = 1 2 mv 2 0 + mgh correct 2. K f = mg h - 1 2 mv 2 0 3. K f = 1 2 mv 2 0 - mgh 4. K f = 1 2 mv 2 0 5. K f = mg h Explanation: By the work-energy theorem, K f - K i = W , where in the present problem, W = ( mg ) h and K i = 1 2 mv 2 0 . Thus, K f = K i + W = 1 2 mv 2 0 + mg h . 003 (part 1 of 4) 10.0 points A bead slides starting from rest at position O on a frictionless wire. The gravitation field is in the - y direction. x y Z S Y O At which position(s) will the speed of the bead have a maximum value? 1. Point Z . 2. Point S . 3. Point Y . correct 4. The bead remains stationary at point O . 5. Points Z and Y . Explanation: Since the total energy is constant, the max- imum kinetic energy will occur when the po- tential energy is a minimum. Thus point Y is the correct answer.

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burgin (lcb626) – HW06 – markert – (56480) 2 004 (part 2 of 4) 10.0 points At which position(s) will the magnitude of the acceleration in the x direction of the bead have a maximum value? 1. Points Z and Y . 2. Point Z . 3. Point S . 4. Point Y . 5. Point O . correct Explanation: The acceleration is maximum at point O . The acceleration is along the path of the wire at point O . Therefore the x component of the acceleration is greatest at point O . 005 (part 3 of 4) 10.0 points At which position(s) will the speed of the bead have a minimum value? 1. Point S . correct 2. The bead’s speed is constant. 3. Points Z and Y . 4. Point Y . 5. Point Z . Explanation: Since the total energy is constant, the min- imum kinetic energy will occur when the po- tential energy is a maximum. Thus point S is the correct answer.
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