Your friend has just been in a traffic accident and is trying to negotiate with the insurance company of the other driver to pay for fixing her car. She believes that the other car was speeding and therefore the accident was the other driver's fault. She knows that you have a knowledge of physics and hopes that you can prove her conjecture. She takes you out to the scene of the crash and describes what happened. She was traveling North when she entered the fateful intersection. She looked in both directions and did not see another car approaching. It was a bright, sunny, clear day. When she reached the center of the intersection, her car was struck by the other car which was traveling East. The two cars remained joined together after the collision and skidded to a stop. The speed limit on both roads entering the intersection is 50 mph. From the skid marks still visible on the street, you determine that after the collision the cars skidded 56 feet at an angle of 30 degress north of east before stopping. She has a copy of the police report which gives the make and year of each car. At the library you determine that the weight of her car was 4000 lbs and that of the other car was 3600 lbs, where you included the driver's weight in each case. There were no other passengers. The coefficient of kinetic friction for a rubber tire skidding on dry pavement is 0.8. The other driver's insurance agent, trying to find an excuse to deny claim to your friend, insists that it is not enough to prove his client was speeding, so your friend must also show that she was under the speed limit.(adsbygoogle = window.adsbygoogle || []).push({});

find the speed of your friend's car and the speed of the other driver's car

so first i have to find out the speed right after they crash into each other goin in the 30 deg direction

so i set kinetic energy = the work done by friction since that's the only force there

1/2mv^2-1/2mVinitial^2=-0.8(mg)*D D is the distance traveled after the crash

since v=0 at that point 1/2 Vinitial^2=0.8(g)*D

Vinitial = sqrt(2*0.8*g*D)

and then this part i'm not too sure if it is right

m1v1 = (m1+m2)v cos 30 m1 is the car goin east

m2v2 = (m1+m2)v sin 30

and i plug and solve but i still get the wrong answer... anyone know what i did wrong

okay... nevermind i did a really stupid mistake i switched m1 and m2 so i kept gettin the opposite answer.... sorry

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# Homework Help: Car collision skid mark physics

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