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Re: Car crash mystery
Posted by Erik919kt [Email] (more from Erik919kt) on Tue, 20 Aug 2013 10:24:10
In Reply to: Car crash mystery, No Snaab, Mon, 19 Aug 2013 13:56:21
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I've been crunching some numbers. You guys'll want to check my math.
Anyway, mass of a MB SL = about 1700kg. I'm guessing on that.
converstion factor: 1 mph = 0.447 m/s
60 mph = 26.8 m/s
70 mph = 31.3 m/s
100 mph = 44.7 m/s
I think the car should be able to stop with a 150 ft skid if going 60 mph.
So using E = 1/2 mv2, its energy at 60 mph is 6.2 x 10(to the fifth) kgm2/s2. Too bad I can't do superscripts. This means that 150 ft of skid marks dissipates this amount of energy, since the car is stopped (zero kinetic energy) at the end of the skid.
At 100 mph, E = 1.72 x 10(to the sixth)
Laying down 150 ft of skid marks at 100 mph dissipates 6.2 x 10(to the fifth) amount of energy, leaving us with 1.1 x 10(to the sixth) kgm2/s2. Solving for v, the car is still going 35.7 mph after laying down the skid marks. I'm not sure this is enough to do the damage you witnessed, not and have the car continue on into your street.
Interestingly, laying down 150 ft of skid marks at 70 mph leaves us with a residual speed of 16 mph. He could not have taken out the trees at 16 mph, IMHO. He would have stopped at the trees.
So then, I'm guessing the initial speed was in excess of 100 mph. Residual speed after 150 of skid marks from 110 mph would have been 41.2 mph, and from 120 mph, 46 mph. I'm voting for 120 mph.
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