Faster moving objects have a larger force acting on them.

A refrigerator is pushed across the floor, to the east, such that it speeds up by 1 cm/s each second as it moves. Which of the following best describes the net force acting on the refrigerator? Explain your choice.

a. It is increasing.

b. It is constant.

c. It is decreasing.

d..Can't be answered without more information about the force/refrigerator.

 Correct Answer

Sue and Eve are each pushing a refrigerator across a floor. Sue's refrigerator moves across the floor at a rate of 10 cm every second, while Eve's moves at 30 cm every second. Which of the following statements is always true? Explain your choice.

a. Eve's refrigerator has a larger net force acting on it.

b. Sue's refrigerator has a larger net force acting on it.  

c. Net force is the same on both refrigerators.

d. Can't be answered without the mass of the each of the refrigerators.

 Correct Answer

Students who suffer from this misconception will answer a for both questions. In the first question, as the object speeds up they will see a need for an increasing force to keep accelerating it. While in the second question, Eve's refrigerator is simply moving faster than Sue's.

Related misconceptions/student difficulties that may arise in the question:

An object with a constant net force will have a constant speed.

A constant force accelerates a body, until the body uses up all the power of the force.

The net force must be in the direction of motion, so objects will travel along a line in that direction.