# If an object with a mass of #10 kg # is moving on a surface at #15 ms^-1# and slows to a halt after # 4 s#, what is the friction coefficient of the surface?

##### 1 Answer

#### Answer:

The acceleration of the object is

#### Explanation:

First we calculate the acceleration of the object:

where

Rearranging:

The negative sign just shows that it is a deceleration, and we can ignore it for the rest of this calculation.

Now we find the force acting to slow the object, using Newton's Second Law :

This is simply the frictional force acting. Frictional force is related to the normal force acting on the object, which in this case is the weight of the object,

Rearranging and substituting in the force:

Note that