Jack and Jill are driving down a concrete road in a car on a dry day. The car's weight including Jack and Jill is 10,000 N. What is the frictional force between the rubber tire and concrete road?

1 Answer
Miguel F.
Dec 26, 2015

The frictional force is given by the normal force, due to the weight of the car (plus Jack and Jill). Its value is 8000 N.

Explanation:

Frictional force between two surfaces depends on the normal force, #N#, exerted on any body by the surface it is above. It is equal to the component of the weight perpendicular to It depends also on a coefficient, called coefficient of friction, #mu#, which depends on the material and must be tabulated.

#F_"frictional" = mu N"#

I have searched on the Internet, and I found this website, where many coefficients of frictions are tabulated. The coefficient which we want is the one which appears in the second row of the table (rubber/concrete).

There are two coefficients:

  • Static coefficient, which refers to the frictional force exerted when the car is stopped.
  • Kinetic coefficient, which refers to the frictional force exerted when the car is moving (a little lower than static coefficient). This is the one which we will use.

Frictional force can be obtained by:

#F_"frictional" = mu N = mu w = 0.8 cdot 10 000 " N" = 8 000 " N"#

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