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Car Crash!

DavidStack

Entry posted by DavidStack

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As we dive into impulse and momentum in this independent physics unit, I am reminded of my only car "crash" I've ever experienced, if you can even call it that. When I was backing up in a small parking lot several months ago, the back of my car bumped into a small pole that I didn't see, jerking my car to a stop. Due to the minimum speed my car was moving at (5 mph or 2.24 m/s), my car was not damaged at all. So I was interested in finding out what speed it would have been damaged. Given that the car accelerates from 0 m/s to the collision speed in 1 second, its acceleration will equal the collision speed. The force of the collision is measured by F = ma, and with a mass of 1000 kg (close to the mass of my Toyota Corolla), F = 1000 * a. A 1000 kg car can withstand an impulse of about 1000 N*s without damage, so with a collision time of .2 seconds (for the car, not the driver), and the equation J = F * change in time, J = 1000 * a * .2. Thus, 1000 = 200 * a, meaning that the car can top out at an acceleration of 5 m/s^2, or a collision speed of 5 m/s (11.2 mph), without damaging the car if the car starts from rest.

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