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a 2500 lb car is driving down a 10 deg slope at 45 mph. the coefficient...

a 2500 lb car is driving down a 10 deg slope at 45 mph. the coefficient of dynamic friction is .8 between road and tires. the driver Dees an obstacle 30 m ahead and slams on brakes. how fast is the car moving when it hits the obstacle?

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Answer #1

2500 lb = 1134 kg and 45 mph = 20.12 m/s

Normal reaction N = mg cos(T) = 1134*9.8*cos(10) = 10945 N

Friction force = 0.8N = 8756 N

Acceleration due to friction = F/M = 7.72 m/s2

Acceleration due to gravity = g sin(10) = 1.7 m/s2

Net acceleration backwords = 7.72 - 1.7 = 6.02 m/s2

v2 = u2 + 2as thus

v2 = 20.1*20.1 - 2*6*30

v = 6.7 m/s.

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