<p>Two cars collide at an intersection. Car A, with a mass of 2000 kg, is going
ID: 1972583 • Letter: #
Question
<p>Two cars collide at an intersection. Car A, with a mass of 2000 kg, is going from west to east, while car B, of mass 1500 kg, is going from north two south at 15 m/s. As a result of this collision, the two cars become enmeshed and move as one afterward. In your role as an expert witness, you inspect the scene and determine that, after the collision, the enmeshed cars moved at an angle of 65<sup>o </sup>south of east from the point of impact. Find the speed of car A just before the collision and the speed of the enmeshed cars just after the collision. </p>Explanation / Answer
This describes a perfectly inelastic collision. Car A was moving only in x and Car B was moving only in y, which is convenient. Car B had y-momentum of (1500 kg)(14 m/s) = 21000 kg-m/s in the south direction, which must therefore also be the y-momentum of the Cars AB enmeshed mass. If the cars' angle of motion together was 65 degrees south of east, the cars' momentum must also be in this direction. That momentum has a y-component of 21000 kg-m/s, so, using trigonometry, the x-component must be (21000 kg-m/s) / tan(65). Then, knowing the x- and y-components of the momentum, the total momentum can be found using the Pythagorean Theorem; it would be the square root of the sum of the squares of the components. Divide that momentum by the combined mass of the cars, 3500 kg, to answer part A. To answer part B, just recognize that the x-momentum of Cars AB is the same as the original momentum of Car A. You already know that momentum, so simply divide it by the mass of Car A, 2000 kg, to get the car's original speed.
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