##### # Unit 6, Quiz #1 1. If there is a net force acting upon an object, then the object is at rest. the object is moving with a constant velocity. the object is accelerating. either a or b.   2. The difference between speed and velocity is that speed is a vector and velocity is a scalar. speed is a scalar and velocity is a vector. speed is a magnitude and velocity is a direction. speed is a distance and velocity is an accleration. none of these.   3. If an object is moving in a circle, then it is moving with a constant velocity. it is accelerating. the forces acting upon it are balanced. only the centripetal and the centrifugal forces are balanced.   4. A physics teacher ties an eraser to the end of a string and then whirls it in a clockwise circle. If the teacher lets go of the string, then the eraser hits a student in the classroom. If the string is let go when the eraser is at point X on the diagram at the right, then which student in the class will the eraser hit? Write the initials in this space: ________________ Once the teacher lets go of the string, it moves along a specific path. What kind of force causes the can to move in the path which it moves once the string is let go of - centripetal, centrifugal, or no force? _________________ Support your answer using complete sentences and solid physics reasoning.   5. In the diagram at the right, draw vector arrows (straight lines) which indicate the following for an object which is moving in a counterclockwise circle. a. the velocity at point A. b. the net force at point B. c. the acceleration at point C.       6. Siblings Aileen and Ben Dover make the turn on the Shock Wave at Great America. Their 400 kg car moves with a speed of 20 m/s through a curve which has a radius of 20.0 meters. A free-body diagram (as viewed along the incline) is shown in the diagram at the right. The normal force has been resolved into vertical and horizontal components. Use Newton's laws and your understanding of ciruclar motion to determine the following. To maximize the amount of partial credit, show your work in the space below. a= __________ Fgrav = __________ Fhoriz = __________ Fnet = __________ Fvert = __________ Theta = __________   7. Construct a free-body diagram showing the direction and types of forces acting upon the car at the top and the bottom of a loop. Be sure to label the forces according to type. Bottom: Top:   Anna experiences a downward acceleration of 24.0 m/s2 at the top of the loop and an upwards acceleration of 12.0 m/s2 at the bottom of the loop. Use Newton's second law to fill in all the blanks and to ultimately determine the normal force acting upon Anna's 800 kg roller coaster car. PSYW Bottom Top Fnet = _____________ Fgrav= _____________ Fnorm= _____________ Fnet = _____________ Fgrav= _____________ Fnorm= _____________
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Last updated on 12/14/98.