A 1000 kg automobile is traveling at an initial speed of 20 m/s. It is brought to a complete stop in 5 s over a distance of 50 m. What is the work done in stopping the automobile

W = -2*10⁵ J

Explanation:

Assuming no friction present, we can find the work done by an external force stopping the car, applying the work-energy theorem.This theorem says that the total work done on one object by an external net force, is equal to the change in the kinetic energy of the object.If the automobile is brought to a complete stop, we can find the change of the kinetic energy as follows:

       

So, the total work done in stopping the automobile, is -2*10⁵ J. The minus sign stems from the fact that the force and the displacement have opposite directions.