Introduction to Physics I

• in direction? They have opposite directions. G. Explain how your answers to part F are consistent with Newton’s third law and the impulse- momentum theorem (F net ∆ t = ∆ p) for: • each astronaut considered separately, and The net force on astronaut A is equal and opposite of the net force on astronaut B since the only force acting on either astronaut is a member of a Newton’s third law pair. Multiplying by the time yields equal and opposite change in momentum vectors as in part F above. • for the system of both astronauts together. The change in momentum for the system of two astronauts is the sum of the changes in momentum for each one. This gives zero change in momentum for the system since the individual changes in momentum are equal and opposite. This makes sense as the net force on the system is also zero. IV. In experiment 1, two hands push identical blocks of mass m toward each other across a level, frictionless surface with a constant force of magnitude F o over the interval from t 1 to t 2 . In this problem, you will consider 4 other experiments in which the setup differs from that in experiment 1. In each experiment, both blocks start from rest at time t 1 on a level, frictionless surface; both hands exert the same magnitude force, F o , over the interval from t 1 to t 2 ; and the blocks do not run into each other during this interval. In each experiment, consider the net work done during the interval from t 1 to t 2 by external forces on the system that consists of the blocks and any spring or rod that may be connecting them. Experiment 1 m m Written homework 9 Physics 101 - Andrew Crouse - Ithaca College Fall Adapted from: Tutorials in Introductory Physics, McDermott, Shaffer, & P.E.G., U. Wash. https://www.coursehero.com/file/9170223/HW9-SOL/ This study resource was shared via CourseHero.com A. In experiment 2, the hands push in the same direction. Is the net external work on the system of the two blocks in experiment 2, greater than, less than, or equal to that in experiment 1? Explain. Each hand exerts a force in the direction of the displacement. The forces and distances are the same. So, the same work is done. B. In experiment 3, the blocks are connected by a spring. The spring is initially neither stretched nor compressed. Is the net external work on the system of the two blocks and the spring in experiment 3 greater than, less than, or equal to that in experiment 1? Explain. The blocks don’t travel as far in the time interval. So, less work is done. C. In experiment 4, the mass of one of the blocks is m /2. Is the net external work on the system of the two blocks in experiment 4 greater than, less than, or equal to that in experiment 1? Explain. More work is done because the rightmost block travels farther. D. In experiment 5, the blocks are connected by a rigid rod ( i.e., a rod that can not compress). Is the net external work on the system of the two blocks and the rod in experiment 5 greater than, less than, or equal to that in experiment 1? Explain. No work is done. There is no displacement. V. Two identical blocks, A and B, on a frictionless surface are connected by a spring of negligible mass. The spring is initially unstretched. During the interval from t 1 to t 2 , block A is pushed through a distance d A by a hand exerting a force of magnitude F A , as shown. Block B is held in place by a wall. The wall exerts a force on block B that varies with time but is always directed to the left. A. During the interval from t 1 to t 2 : 1. Is the work done on block A by the hand positive, negative, or zero? Explain. The work is positive. The force is in the same direction as the displacement. 2. Is the work done on block B by the wall positive, negative, or zero? Explain. Experiment 2 m m Experiment 3 m m Experiment 4 m m /2 Experiment 5 m m Rigid rod A A t = t 1 t = t 2 The hand exerts a constant force of magnitude F A B B d A d A Written homework 9 Physics 101 - Andrew Crouse - Ithaca College Fall Adapted from: Tutorials in Introductory Physics, McDermott, Shaffer, & P.E.G., U. Wash. https://www.coursehero.com/file/9170223/HW9-SOL/ This study resource was shared via CourseHero.com

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