You have been called to testify as an expert witness in a trial involving a head

Question

You have been called to testify as an expert witness in a trial involving a head-on collision. Car A weighs 1515 lb and was traveling eastward. Car B weighs 1125 lb and was traveling westward at 47.0 mph. The cars locked bumpers and slid eastward with their wheels locked for 19.5 ft before stopping. You have measured the coefficient of kinetic friction between the tires and the pavement to be 0.750. How fast (in miles per hour) was car A traveling just before the collision? (This problem uses English units because they would be used in a U.S. legal proceeding.) Number mph

Explanation / Answer

weight of car 1 = 1515 lb, was travelling eastwards with speed = u
weight of car 2 = 1125 lb, was travelling west wards with speed, v = 47 mph = 68.9333 ft/s
the cars locked and moved eastwards for d = 19.5 ft before stopping with weheels locked
coefficient of kinetic friction, k = 0.75
now, when the two cards locked, total fricitonal acceleration = k(W1 + W2)g/(W1 + W2) = kg
hence if after collsiion velocity of cars is v'
2*kg*d = v'^2
2*0.75*32.2*19.5 = v'^2
v' = 30.689 ft/s

hence now from conservation of momentum
W1u - W2v = (W1 + W2)v'
u = [(2640)30.689 + 1125*68.933]/1515
u = 104.66673 ft/s = 71.363 mph

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.