1. At the end of the tutorial Superposition and reflection of pulses, you observ
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1. At the end of the tutorial Superposition and reflection of pulses, you observed a demonstration of A row of paper cups was placed near a spring as a pulse reflected from the free end of a spring. show n in the top-view diagram below. À pulse with a maximum displacement slightly less than the cup-spring distance was sent down the spring. Cups Top view On the diagram, indicate which cup(s) were hit by the spring during the demonstration. a. Incident pulse- b. On the basis of your observation, did the free end of the spring have a maximum displacement that was greater than, less than, or equal to the maximum displacement of the incident pulse? On the basis of your answer above, were the incident and reflected pulses on the same side of the spring (e g., both on the cup side) or on opposite sides of the spring (e-g, one on the cup side and one on the other side)? Explain your reasoning. c. In the tutorial Superposition and reflection of pulses, we developed a model that we can use to predict the shape and orientation of a pulse reflected from the fixed end of a spring. We can develop a similar model for free-end reflection. In this case as well, we imagine that the spring extends past the free end. We then imagine sending a pulse with the appropriate shape and location on this imaginary portion of spring toward the incident pulse so that, as the pulses pass each other, the appropriate boundary condition at the free end is satisfied. 2. Consider a pulse incident on the free end of a spring as | Before i-W.LLI- shown. Note that the leading edge of the pulse is 2 squares wide and the trailing edge is 4 squares wide. Free end a. Would the reflected and incident pulses be on the same side of the spring or on opposite sides? Would you expect the incident and reflected pulses to After have the same leading edge or different leading edges? Explain your reasoning. (Hint:Which part of the pulse hits the boundary first?) Free end b. Sketch the shape of the reflected pulse on the diagram at right. © ntorials in Introductory Physics, Physics Education Group, Department of Physics University of Washington (Autumn 2017, Mazur version)Explanation / Answer
1. a) In superposition and reflection of pulse, there is a pulse reflected from the free end of a spring. The pulse reflects off the free end and return in the same direction of displacement. So, the pulse is not inveretd and the amplitude of reflection is added to the remaining part of the incident pulse. Hence, the last cup nearest to the end is hit by the reflected pulse.
b) As the pulse is reflecting from the free end and the amplitude of the reflection is added up with the incident pulse amplitude. Hence, the free end of the spring had a maximum displacement greater than the amplitude of the incident pulse.
c) The reflection of the pulse is not inverted when the incident pulse comes to the end, it reflects back in the opposite direction of the same side of the spring. Hence, the reflected pulse is in the same side with the maximum displacement as the incident pulse.
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