Sliding friction

Homework Statement

So say there was some object on a Horizontal surface. id there was some force on (not constant, but a hit or something) this object and there was a sliding friction between the surface and the object. How would that factor in to the F=ma formula? and what if you are given a mass, and a distance that the object moved (not acceleration), and sliding friction coefficient of course - how would you find the force?

Homework Equations

F=ma

Nuk (N)= Force of Friction

The Attempt at a Solution

Would it be F - F(of friction) = m (a)?

converting that accel to a distance is what is bothering me a lot :/

cepheid
Staff Emeritus
Gold Member
Hello,

The F in F = ma is always the NET force acting on the object. So, yes, in the beginning, when a force is briefly applied to accelerate the object, the equation would be:

Fapplied - Ffric = ma

Once the applied force has ceased, and the object slides to a stop under friction, it is just:

-Ffric = ma

The kinematics equations you probably know are only applicable for constant acceleration. In this situation, the acceleration is not constant, because the net force is not constant with time. For a brief period at the beginning, it includes the initial "hit", and afterwards, it includes only friction. So, you need more information in order to figure things out.

If you knew what final speed the object reached at the end of the initial "hit" (the period during which it was accelerating), and you know the distance over which it travelled *after* reaching that max speed, then this reduces to a standard kinematics problem and you can solve for the decelerating frictional force.

cepheid
Staff Emeritus