IC7.1-CarBumper

IC7.1-CarBumper - N mg kx Write Equations for each term. 4...

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Lesson 7 In Class 7.1 Car Bumper Design Bumper Test
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3/111 You want to bring the 3500 lb car to a stop from a speed of 5 mph. You want it to stop in a distance of 6 inches, so find the stiffness of the two springs behind the bumper. The two springs are undeformed at the start of the impact. What is your first step? IC7.1 Car Bumper Design Solution: Problem Type: Find: Given: W=3500 lbs, v 1 = 5 mph, v 2 =0 mph, x 2 = 6 inches k: Spring rate for each of the two springs Work Energy Write out the Work Energy Relationship T 1 + U 1-2 = T 2 A FBD will help us determine which forces might be doing work. Substitute into W-E Equation Reflection:
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Unformatted text preview: N mg kx Write Equations for each term. 4 U ) 2 1 ( U U ) ( 2 d U 2-1 2 2-1 2 2-1 2-1 k k kx dx kx f x-=-=-=-= = 2 1 r r r F Two springs 7 . 2922 ) 3600 5280 5 )( 2 . 32 3500 ( 2 1 2 1 2 1 2 1 2 1 = = = = T lbs ft T T mv T in lbs k ft lbs k k / 2 . 974 / 8 . 690 , 11 4 7 . 2922 = = =-Get mass W/g mph to ft/sec Puts k in lb/in. Okay if you decide to leave it in lb/ft Takes almost a ton to compress springs 1 in. Remember there are two springs. Seems reasonable, although 6 inches would likely do some damage to a typical car! Sketch:...
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This note was uploaded on 01/22/2011 for the course ME 212 taught by Professor Staff during the Spring '05 term at Cal Poly.

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IC7.1-CarBumper - N mg kx Write Equations for each term. 4...

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