# 21 - hernandez(ejh742 – oldhomework 21 – Turner...

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Unformatted text preview: hernandez (ejh742) – oldhomework 21 – Turner – (58120) 1 This print-out should have 9 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A large wedge (with a rough inclined sur- face and a smooth lower surface) rests on a horizontal frictionless surface. A block with a rough bottom starts from rest and slides down the inclined surface of the wedge. The coefficient for friction between the block and inclined wedge surface is . 1 < μ block incline < . 5 and that between the lower wedge surface and horizontal surface is zero. While the block is sliding down the inclined surface, the combined center of mass of the block and wedge 1. moves horizontally with increasing speed 2. moves both horizontally and vertically with increasing speed 3. cannot be determined 4. moves vertically with increasing speed correct 5. moves vertically with constant speed 6. moves both horizontally and vertically with constant speed 7. does not move 8. moves horizontally with constant speed Explanation: Basic Concepts: Momentum Solution: The motion of the center of mass of a system is only affected by the external forces acting on the system, and not by any internal forces such as the friction between the block and wedge. The net external force on the system acts only in the vertical direc- tion, so the center of mass will not move in a horizontal direction. The fact that the block starts from rest tells us that it must be accel- erating. Since one component of the system (the block) has a component of acceleration in the vertical direction and the other compo- nent (the wedge) does not, we know that the center of mass must be accelerating. The net external force on this system acts only in the vertical direction. Therefore, while the block is moving, the center of mass of the block and wedge must be moving downward with increasing speed....
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21 - hernandez(ejh742 – oldhomework 21 – Turner...

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