Transcript Slide 1
Consider a person standing in an elevator that is moving upward at constant speed. The magnitude of the upward normal force, N, exerted by the elevator floor on the person's feet is A. larger than B. the same as C. smaller than the magnitude of the downward weight, W, of the person. speed v Sandy and Fred are having a tug-of-war. So far, no one is winning. Sandy Fred Q1: What is the direction of the force of friction on Sandy's feet A) Right B) Left Q2: How large is the force of friction on Sandy's feet the force of friction on FF Fred's feet? A. FS F F B. FS FF C. FS FF comparedFSto FS An Atwood's machine is a pulley with two masses connected by a string as shown. The mass of object A, mA , is twice the mass of object B, mB. The tension T in the string on the left, above mass A, is... A. T = mA g B. T = mB g C. Neither of these. A B RI-2. An elevator is going up at a constant speed. Near the top floor, it starts to slow to a stop. During the period that it is slowing down, its acceleration is A) downward B) upward. C) in some other direction. RI-5. A student is asked the following question on an exam: A car is moving at 90mph and suddenly brakes with a constant acceleration a = – 2g to a full stop. How many seconds does the car take to stop? Which equation can be used to answer the question? A) B) C) RI-6. Consider the vector Which equation is correct? RI-9. A particle is moving with constant acceleration. Its velocity vector at two different times is shown below. What is the direction of the acceleration? RI-13. Conical pendulum At the instant shown, which free-body diagram best indicates the forces acting on the pendulum. Which is larger ? A) the weight mg or B) the tension T? CT6-6. A mass m is pulled along a rough table at constant velocity with an external force Fext at some angle above the horizontal. The magnitudes of the forces on the free-body diagram have not been drawn carefully, but the directions of the forces are correct. N Fext Ffric Which statement below must be true? A. B. C. D. E. Ffric > Fext , Ffric < Fext , Ffric > Fext , Ffric < Fext , None of these. N N N N > < < > mg. mg. mg. mg. mg CT6-7 A mass slides down a rough inclined plane with some non-zero acceleration a1. The same mass is shoved up the same incline with a large, brief initial push. As the mass moves up the incline, its acceleration is a2. How do a1 and a2 compare? v v a2 a1 A) a1 > a2 B) a1 = a2 C) a1 < a2 CT6-8. A car rounds a banked curve at some speed without skidding. The radius of curvature of the curve is R. A possible free-body diagram (which may or may not be correct) is shown. N a Ffric mg What can you say about Ffric, the magnitude of the force of friction? A) Ffric s N B) Ffric K N C) Neither CT6-8. A car rounds a banked curve at some speed without skidding. The radius of curvature of the curve is R. A possible free-body diagram (which may or may not be correct) is shown. N a Ffric mg What can you say about the direction of Ffric? A. It is in the direction shown in the free-body diagram. B. It is in the direction opposite shown in the diagram. C. The direction depends on the speed of the car. CT6-3.. A mass m accelerates downward along a frictionless inclined plane. The magnitudes of the forces on the free-body diagram have not been drawn carefully, but the directions of the forces are correct. N a mg A. B. C. Which statment below must be true? mg > N N > mg N=mg CT6-5. A rider in a "barrel of fun" hinds herself stuck with her back to the wall. Which diagram correctly shows the forces acting on her? A)Pink B)Blue C)Green D) Purple E)Yellow