A car of weight W = 10.0 kN makes a turn on a track that is banked at an angle of θ = 20.0°. Inside the car, hanging from a short string tied to the rear-view mirror, is an ornament. As the car turns, the ornament swings out at an angle of φ = 30.0° measured from the vertical inside the car. What is the force of static friction between the car and the road?

THINK:
The static frictional force between the car and the road can be calculated by considering the forces acting on the ornament. The forces acting on the ornament are tension force, the gravitational force and the net centripetal force acting towards the center of the car track.
SKETCH:
The sketch for the given problem is shown in the below figure
RESEARCH:
The tensional force on the string can be resolved into two components, and then the horizontal component of the tension provides the centripetal force on the ornament. The centripetal force depends on the mass of the ornament (
) and the square of the linear speed (
) and the radius of the circular path of the ornament (
). Hence, the horizontal component of the tension is
…… (1)
Now, the vertical component of the tensional force is balanced by the weight (
) of the ornament.
…… (2)
The static frictional force acting between the car and the road is the product of the coefficient of the friction (
) and the weight of the car (
). So

Here
is the mass of the car and
is the acceleration due to gravity.
Here the static frictional force provides the centripetal force acting on the car. Hence
…… (3)
SIMPLIFY:
Using equations (1) and (2), we get
…… (4)
From equations (3) and (4), we get the frictional force acting between the road and the car.
…… (5)
Given data:
The weight of the car is

The banking angle of the turn of the car, 
The ornament angle with the normal,
CALCULATE:
Now, substituting the numerical values in the equation (3), we get the static frictional force between the car and the road.
