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Energy-Impulse Model

Energy-Impulse Model

Q Two carts of unequal mass (mA > mB) move on friction-less tracks as shown. Both start from rest and have the same constant force applied to them until they reach the finish line. The force begins on Cart A first. The force on Cart B begins the instant Cart A is even with it. Both carts reach the finish line at the same time. At the finish Cart B is moving faster than Cart A. 1. At an instant when both carts have the force exerted on them, is the acceleration of cart A greater than, less than, or equal to the acceleration of cart B? Explain. 2. Is the magnitude of the final momentum of Cart A greater than, less than, or equal to the magnitude of the final momentum of Cart B. Explain/Justify your answer. 3. Is the final kinetic energy of Cart A greater than, less than, or equal to the final kinetic energy of Cart B. Explain/Justify your answer. Rubric Modeling Modeling Criteria Ratings Pts This criterion is linked to a Learning OutcomeAccuracy All the ideas used in the diagram and/or narrative correspond to ideas established by the class thus far. (No ideas are used that have not been previously established and agreed on.) 5 pts This criterion is linked to a Learning OutcomeCompleteness All the established ideas and assumptions necessary to explain the event are included in the diagram and/or narrative. (No relevant ideas are missing.) 5 pts This criterion is linked to a Learning OutcomeClarity and Logical Reasoning The presentation is well done so that it flows logically and is easy to follow. It also explicitly connects the relevant ideas to the event being explained. 5 pts Total Points: 15 PreviousNext

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1. When the force is applied to Cart A, it accelerates from rest until it reaches the same point as Cart B. At this point, Cart B also experiences the force and begins to accelerate. Since Cart B has a smaller mass than Cart A, the same force will cause it to accelerate more, as given by Newton's second law of motion (F=ma). Therefore, the acceleration of Cart B will be greater than the acceleration of Cart A at the instant when both carts have the force exerted on them. 2. Both carts start from rest and have the same constant force applied to them until they reach the finish line. Since the carts reach the finish line at the same time, they will have the same final momentum in the absence of any external forces acting on them. However, there is a force applied to both carts, which will cause their momentum to change