Map Kesten Tauck presented by Sapling Leaming You have been called to testify as

Question

Map Kesten Tauck presented by Sapling Leaming 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 17.5 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 - O Previous Give Up & View Solution Q Check Answer ) Next Exit Hint

Explanation / Answer

here,

mass of car A , mA = 1515 lb

mass of car B , mB = 1125 lb

initial speed of car B , uB = - 47 mph

uk = 0.75

accelration , a = uk * g = 7.36 m/s^2

s = 17.5 ft = 5.32 m

let the final speed after the collison be v

v = sqrt(2 * a * s ) = sqrt(2 * 5.32 * 7.36) m/s

v = 8.85 m/s = 19.8 mph

let the initial speed of car A be uA

for collison

using conservation of momentum

mA * uA + mB * uB = (mA + mB) * v

1515 * uA - 47 * 1125 = ( 1515 + 1125) * 19.8

solving for uA

uA = 69.4 mph

the speed of car A before the collison is 69.4 mph

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