A 1,990-kg automobile starts from rest at point A on a 7degree incline and coast
ID: 1849067 • Letter: A
Question
A 1,990-kg automobile starts from rest at point A on a 7degree incline and coasts through a distance of 143m to point B. The brakes are then applied, causing the automobile to come to a stop point C, 19m from B. Knowing that slipping is impending during the braking period and neglecting air resistance and rolling resistance, determine (a) the speed of the automobile at point B, (b) the coefficient of static friction between the tires and the road.
I found thatthe speed at Point B is 18.49 m/s. I need help finding the coefficient of friction.
Explanation / Answer
To find the coefficient, we need to find the force of friction. to find that we can find the acceleration during braking. To find acceleration, we use the equation: Vf^2 = Vi^2 + 2ad From point B to Point C 0 = (18.49)^2 + 2*a*(19) a = -9.00 m/s^2 We know that the net force on the car can be calculated by: F=ma so, F = m(-9.00) We also know the equation for force of friction is: F = sN where s is the coefficient and N is the normal force. The normal force is just mg, so we have F = smg Now we can combine these equations and solve for s. smg = m(-9.00) sg = -9.00 s = -9.00/g s = 0.92
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