High Banked Turn

A stock car of mass 1400 kg 1400\text{ kg} is racing around a speedway with banked turns. The car and turn are shown in the figures below.

  • Its wheelbase is a rectangle with width 170 cm 170\text{ cm} , and its center of mass is centered in that rectangular wheelbase.
  • With the car sitting on the level road, its center of mass is 50 cm 50\text{ cm} above the road surface.
  • The car has a velocity through the turn of 40 m/s 40 \text{ m/s} .
  • The turn radius is 100 m 100\text{ m} .
  • The bank angle of the track surface in the turn is 3 0 30^\circ .

Find the combined force normal to the track surface exerted on the right side tires.

Express your positive answer (in Newtons) as the force on the right front plus the force on the right rear.

Details and Assumptions :

  • Take g = 10 m/sec 2 g = 10\text{ m/sec}^2 .
  • Ignore possible aerodynamic forces.
  • Ignore possible tangential accelerations due to throttle or brake.
  • Ignore possible center of mass movement due to suspension movement.
  • Ignore possible gyroscopic effects from rotating mass in engine or wheels.
  • The car is turning left.


The answer is 15310.

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1 solution

Matt Owings
Aug 12, 2016

While negotiating the banked turn, there are 3 forces acting on the car: gravity, centrifugal force, and the ground reaction forces the track surface exerts on the tires.

Gravity exerts a force of m g m g and always acts vertically downward.
Centrifugal force is given by mass m v 2 R \frac{m v^2} {\text{R}} and acts radially outward in the plane of motion, the horizontal plane in this problem.
Ground reaction forces (GRF) act in 3 dimensions at each tire contact with the track. We will only consider GRF normal to track surface in this problem.

The mass of the car is 1 400 kg \SI{1400}{ \kilo \gram} so if g = 10 m/s 2 g=10 \text{m/s}^2 , then gravitational force is 14 000 N \SI{14000}{\newton} .
If v v is 40 m/ s 40 \text{m/ s} and R R is 100 100 meters then centrifugal force is 22 400 N \SI{22400}{\newton} .

See figures.

The next step is to resolve each of these vector quantities into components normal to and parallel to the track surface.

The gravitational force has a component normal to track surface of 14000 × cos 3 0 = 12 124 N 14000 \times \cos 30^\circ = \SI{12124}{\newton} . The gravitational force has a component parallel to track surface of 14000 × sin 3 0 = 7 000 N 14000 \times \sin 30^\circ = \SI{7000}{\newton} . Centrifugal force has a component normal to track surface of 22400 × sin 3 0 = 11 200 N 22400 \times \sin 30^\circ = \SI{11200}{\newton} . Centrifugal force has a component parallel to track surface of 22400 × cos 3 0 = 19 400 N 22400 \times \cos 30^\circ = \SI{19400}{\newton} .

Combining these components, we have a normal component of 23 324 N \SI{23324}{\newton} acting into the track surface and a parallel component of 12 400 N \SI{12400}{\newton} acting up the bank.

See figures.

Now to find the GRF acting on the right side tires we will balance the moments about the point of contact of the left side tires with the track surface. This is point P P in the drawing. Gravity and centrifugal force act through the center of mass.

The normal force is 170 / 2 170/2 or 85 cm \SI{85}{\centi\meter} to the right of point P P . It generates a clockwise moment of 19 825 N m \SI{19825}{\newton \meter} about point P P . The parallel component acts through the center of mass which is 50 cm \SI{50}{\centi \meter} above point P P . It generates a clockwise moment of 6 200 N m \SI{6200}{\newton \meter} about point P P .

There is a total clockwise moment of 26 025 N m \SI{26025}{\newton\meter} about P P . The right side normal GRF x 1.70 must generate a counterclockwise moment of magnitude 26 025 N m \SI{26025}{\newton\meter} . So, 26025 1.7 = 15 310 N \dfrac{26025}{ 1.7} = \SI{15310}{\newton}

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