Kaplunovsky - exam 02

Kaplunovsky - exam 02 - midterm 02 – – Due Mar 7 2007...

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Unformatted text preview: midterm 02 – – Due: Mar 7 2007, 10:00 pm 1 Question 1, chap 5, sect 99. part 1 of 2 5 points A spherical mass rests upon two wedges, as seen in the figure below. The sphere and the wedges are at rest and stay at rest. There is no friction between the sphere and the wedges. M The following figures show several attempts at drawing free-body diagrams for the sphere. Which figure has the correct directions for each force? Note: The magnitude of the forces are not necessarily drawn to scale. 1. weight normal normal correct 2. Since the sphere is not moving, no forces act on it. 3. normal normal weight weight 4. normal weight weight 5. normal normal weight weight 6. weight 7. weight friction friction normal normal 8. weight normal 9. weight normal normal Explanation: Weight – the force of gravity – pulls the sphere down. The normal force of the left wedge upon the sphere acts perpendicular to ( normal to ) their surfaces at the point of con- tact; i.e. , diagonally upward and rightward. Likewise, the normal force of the right wedge upon the sphere acts diagonally upward and leftward. Question 2, chap 5, sect 99. part 2 of 2 5 points The wedges themselves lie on a horizontal table. There is friction between the table and the wedges. The following figures show several attempts at drawing free-body diagrams for midterm 02 – – Due: Mar 7 2007, 10:00 pm 2 the left wedge. Which figure has the correct directions for each force? Note: The magnitude of the forces are not necessarily drawn to scale. 1. normal weight friction F s p h e r e 2. normal weight friction F s p h e r e 3. normal weight friction F s p h e r e 4. normal weight friction F s p h e r e correct 5. Since the sphere is not moving, no forces act on it. 6. normal weight F s p h e r e 7. normal weight F sphere f r i c t i o n 8. normal weight F sphere f r i c t i o n 9. normal weight F s p h e r e Explanation: The wedge’s weight pulls it straight down. The force of the sphere upon the wedge is the reaction to the force of the wedge upon the sphere, hence vector F sphere pushes diagonally downward and leftward. The normal force of the table upon the sphere acts straight up, perpendicular to the table’s horizontal surface. Finally, the friction force pushes the wedge rightward in order to prevent it from sliding to the left due to vector F sphere . Question 3, chap -1, sect -1. part 1 of 1 10 points A block with a pulley attached slides along a frictionless surface. It is connected by a string to a second block as shown in the pic- ture below. midterm 02 – – Due: Mar 7 2007, 10:00 pm 3 1 2 no friction Given: the mass of the first block m 1 = 8 kg; the mass of the second block m 2 = 2 kg; g = 9 . 8 m / s 2 . Both pulleys are frictionless and have negligible masses and rotational in- ertias. The string does not stretch, and its mass is negligible. There is no friction be- tween the first block and the table....
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Kaplunovsky - exam 02 - midterm 02 – – Due Mar 7 2007...

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