Print a Calculator Periodic Table stion 15 of 17 Map UNIVERSITY PHYSICS Philip R

Question

Print a Calculator Periodic Table stion 15 of 17 Map UNIVERSITY PHYSICS Philip R. Kesten David L. Tauck prosented by sapling learning 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 46.0 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

By law of conservation of momentum for perfectly inelastic collision,

m1v1i+m2v2i = (m1+m2)vf --------------(1)

When cars skids,

Ff= -uk*(m1+m2)g = (m1+m2)a

a= -uk*g = -0.75*9.81 = -7.34 m/s = -59110 mph^2

Applying kinematic equation,

vf^2 = vi^2 +2ad

d=19.5 ft= 0.003693 miles

when cars stops vf = 0 mph

0 = vi^2 +2*-59110*0.003693     

Gives, vi= 20.9 mph

Thus vf = vi = 20.9mph

Plugging this value in eqn(1)

1515*v1i - 1125*46 = (1515+1125)*20.9

Gives,

v1i = 70.58 mph

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