W091ALLab07

# W091ALLab07 - Physics 1AL Introduction CONSERVATION OF...

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Physics 1AL CONSERVATION OF MOMENTUM Winter 2009 1 Introduction You have a summer job at Amtrak with a group examining the crash between two trains. Your supervisor wants you to calculate the results of two different cases. The first is a perfectly inelastic collision where the two trains stick to each other. The other case is an elastic collision where the two trains bounce of each other with no loss of kinetic energy. Since the trains may be carrying different cargo, their masses may be different. Your supervisor wants you to calculate the final velocity of the trains as a function of the masses and initial velocities of the trains. You decide to calculate the resulting velocities for the system and then build a laboratory model using gliders to check your calculation. Your Objective: To experimentally determine the final velocities of two objects after collision. ______________________________________________________________________________ Pre-lab questions: Read sections 6.1, 6.2, 6.3 in Serway & Faughn Answer each of the following questions in a few sentences of your own words: 1. A 0.75 kg ball is thrown horizontally towards a wall with a speed of 15 m/s. The initial velocity is chosen to be the positive x-direction for this question. The ball horizontally rebounds back from the wall with a speed of 15 m/s in the negative x-direction. What is momentum of the ball before it hits the wall, p i ? What is momentum of the ball after it hits the wall, p f ? What is the change in momentum of the ball, Δ p ? (Give both magnitude and direction for each of the previous answers.) Is momentum conserved for the ball? 2. Perfectly Inelastic Collision . Draw diagrams showing a situation where a bigger, moving train, v i , collides with a smaller train that is not moving. Assume that after the collision the trains stick together. Show separate diagrams for the situation just before the collision and just after the collision. Assume the trains have different masses ( m big and m small ). Make sure you identify your isolated system. Write down the momentum conservation equation for the scenario in question. Solve for the final velocity of the two trains, v f , in terms of v i , m big , and m small . 3. Elastic Collision . Draw two diagrams for the situation where a moving train collides with a train that is not moving, and the trains use their springy bumpers to bounce off each other without damage. One diagram should show the instant just before the collision and the other the instant just after the collision. Assume the trains have different masses ( m moving and m target ) Make sure you identify your isolated system . Solve for the final velocity of each train in terms of the initial velocity of the initially moving train and the two masses. Hint: use conservation of momentum and the relation between the relative velocities before and after collision that arises due to conservation of energy. 4.

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## W091ALLab07 - Physics 1AL Introduction CONSERVATION OF...

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