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Physics 114 Tutorial 5: Tension Instructor: Adnan Khan

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Physics 114 Tutorial 5: Tension Instructor: Adnan Khan • Please do not sit alone. Sit next to at least one student. • Please leave rows C, F, J, and M open. Physics 114 Tutorial 5: Tension Instructor: Adnan Khan 5/7/19 1 Blocks connected by a rope q Section 1: Two blocks, A and B, are tied together with a rope of mass M. Block B is being pushed with a constant horizontal force as shown at right. Assume that there is no friction between the blocks and the blocks are moving to the right. 1. Describe the motion of block A, block B, and the rope. 2. Compare the acceleration of block A, block B and the rope. 5/7/19 2 Blocks connected by a rope 2. Compare the accelerations of block A, block B and the rope. A. aA > aR > aB B. aB > aA > aR C. aA > aB > aR D. aB > aR > aA E. aA = aR = aB 5/7/19 3 Blocks connected by a rope 3. Draw a separate free-body diagram for each block and for the rope. Clearly label your forces. 5/7/19 4 Blocks connected by a rope 4. Rank, from largest to smallest, the magnitudes of the horizontal components of the forces on your diagrams. 5/7/19 5 Blocks connected by a very light string q Section 2: The blocks in section 1 are now connected with a very light, flexible, and inextensible string of mass m (m < M). Suppose the hand pushes so the acceleration of the blocks is the same as in section 1. Blocks have same acceleration as with rope 5. How does the net force on the string compare to the net force on the rope from section 1? A. Fnet, string > Fnet, rope B. Fnet, string = Fnet, rope C. Fnet, string < Fnet, rope 5/7/19 6 Blocks connected by a very light string 6. Is the net force on each of the following greater than, less than, or equal to the net force on the corresponding object or system in section 1 (with the rope). Blocks have same v Block A acceleration as with rope v Block B v The system composed of the blocks and the connecting string. 5/7/19 7 Blocks connected by a very light string 7. Compare the horizontal components of the Blocks have same following pairs of forces: acceleration as with rope v the force on the rope by block A v the force on the string by block A 5/7/19 8 Blocks connected by a very light string 7. Compare the horizontal components of the Blocks have same following pairs of forces: acceleration as with rope v the force on the rope by block B v the force on the string by block B 5/7/19 9 Blocks connected by an essentially massless string 8. Suppose the mass of the string that Blocks have same connects blocks A and B becomes smaller acceleration as with rope and smaller, but the acceleration remains same as in section 1. What happens to: v the magnitude of the net force on that connecting string? v the relative magnitudes of the forces exerted on that connecting string by blocks A and B? 5/7/19 10 The Atwood’s Machine q The Atwood’s machine at right consists of two identical objects connected by a massless string that runs over an ideal pulley. Object B is initially held so that it is above object A and so that neither object can move. 9. Predict the subsequent motions of objects A and B after they are released. Explain the basis for your description. Do not use algebra. 5/7/19 11 The Atwood’s Machine 9. Predict the subsequent motions of objects A and B after they are released. Explain the basis for your description. Do not use algebra. A. Remains stationary B. Oscillates C. Block A moves down D. Block B moves down 5/7/19 12 The Atwood’s Machine 10. Draw separate free-body diagrams for objects A and B. Are your free-body diagrams consistent with your prediction of the motion of the objects? 5/7/19 13 The Atwood’s Machine q Object B is replaced by object C, of greater mass. Object C is initially held so that it is higher than object A and so that neither object can move. 11. Predict: v what will happen to object C when it is released. 5/7/19 14 The Atwood’s Machine q Object B is replaced by object C, of greater mass. Object C is initially held so that it is higher than object A and so that neither object can move. 12. v Do you agree or disagree with the student below? Student: Block A has an upward force of 4N on it, and block C has an upward force of 2N. The weight forces are transmitted through the string onto the blocks. 5/7/19 15.
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