Reporting Category: Motion and Forces Standard: 1.4 - Interpret and apply Newton's three laws of motion.
Standard: 1.6 - Distinguish qualitatively between static and kinetic friction, and describe their effects on the motion of objects.

A 30.0 N force is continuously applied to the right on a 12.0 kg object. The object accelerates on a horizontal frictionless surface. After a certain amount of time, another force of 8.0 N is applied to the left on the object.

Calculate the object’s acceleration before the 8.0 N force is applied. Show your calculations and include units in your answer.

Calculate the object’s acceleration after the 8.0 N force is applied. Show your calculations and include units in your answer.

Is the direction of acceleration in parts (a) and (b) the same or different? Explain your answer.

The object is then pushed onto a slightly rough surface that exerts an additional 20 N frictional force to the left on the object.

Will the object come to rest on the slightly rough surface? Explain your answer.

Scoring Guide and Sample Student Work Select a score point in the table below to view the sample student response.

The response demonstrates a thorough understanding of Newton’s second law of motion. The response correctly calculates the object’s acceleration before and after the 8.0 N force is applied, compares and explains the direction of acceleration, and explains whether the object will come to rest after the addition of 20 N of frictional force.