A theory can help create a model
        
             
        
        
        
Explanation:
A student solving for the acceleration of an object has applied appropriate physics principles and obtained the expression :

Where


m = 7 kg
So, the correct step for obtaining a common denominator for the two fractions in the expression in solving for a is (a) and the value of a is :


Hence, the correct option is (a).
 
        
             
        
        
        
Inertia is when a object in motion will stay in motion or in a standing still state unless acted upon by a unbalancing force.
Friction is when a object slows down because it is rubbing against another object.
If a object is sliding across a surface, theoretically, it would not stop but because it is on a flat surface it would experience friction, this will disperse some of the kinetic energy that it has thus slowing the object down eventually, after some time, to a stop.
Hope this helps! :)