3.A car with a mass of 1500 kg is parked on a hill with an incline of 20°.

Question

a.What is the weight of the car?

b.What is the normal force the car experiences? (hint: balance the forces parallel and perpendicular to the hill using Newton’s second law)

c.What is the magnitude of the force of static friction that keeps the car from sliding down the hill? (hint: balance the forces parallel and perpendicular to the hill)

d.What is the coefficient of static friction? (hint: use the answers you found in b and c to solve for mu. If you did not find answers for b and c, assume N=10000N and f=5000N – note that these are not the correct numbers. They are only here so you can work part d, even if you can’t get b and c)

Answer 1

a. Fc = mg = 1500kg * 9.8N/kg = 14700N.
Wc = 1500kg / 0.454kg/lb = 3304lbs. =
weight of car in lbs.

b. Fv = mgcos20 = 14700cos20 = 13,814N.
= Force perpendicular to the hill.

c. Ff = Fp = Force parallel to the hill.
Ff = Fp = mg*sin20 = 14,700sin20 = 5028N.

d. u = Ff / Fv = 5028 / 13814 = 0.364.