Your accident-reconstruction team has been hired by the localpolice to analyze t
ID: 1745286 • Letter: Y
Question
Your accident-reconstruction team has been hired by the localpolice to analyze the following accident. A careless driver-rearended a car that was halted at a stop sign. Just before the impact,the driver slammed on his brakes, locking the wheels. The driver ofthe struck car had his foot solidly on the brake pedal, locking hisbrakes. The mass of the stuck car was 900 kg, and that of theinitially moving vehicle was 1200 kg. On colllision, the bumpers ofthe two cars meshed. Police determine from the skid marks thatafter the collision the two cars moved 0.76 m together. Testsrevelaed that the coefficient of kinetic energy friction betweenthe tires and pavement was 0.92. The dreiver of the moving carcalims that he was traveling at less than 15 km/h as he approachedthe intersection. Is he telling the truth?Explanation / Answer
Given that the masses of cars is m1 = 900 kg and m2 = 1200kg Initial velocity is U1 =0 and U2 = ? Thedistance travelled is S = 0.76 m The coefficent of kinetic friction is = 0.92 ---------------------------------------------------------------------------- IF thebody is moving in the rough horizotal plane then the accelarationis a = -g Then the distance travelled is Vf2 - Vi2 = 2aS 0 - Vi2 = 2aS -Vi2 =-2gS Vi = 2gS =---------- m/s Apply conservation of momentum before andafter collsioin with the struck car m1U1 + m2*U2 = (m1+m2)V 0 + m2*U2 = (m1+m2)V U2 = (m1+m2)V /m2 = ---------- m/s 1m/s =(1km/1000m)(3600s/1h) = 18/5 km/h If U2 = 15 km/h then he telling the truth.Related Questions
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