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

A refrigerator is pushed across a floor, to the east, at a constant speed. Draw a vector to represent the direction of the net force acting on the refrigerator. If the net force is zero, state that explicitly. Explain your answer.

 Correct Answer

A refrigerator is pushed across the floor, to the east, with a constant net force, also directed to the east. Which of the following best describes the motion of the refrigerator? Explain your choice.

a. It slows down as it moves across the floor.

b. It travels at a constant speed across the floor.

c. It speeds up as it moves across the floor.

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

 Correct Answer

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

Students who suffer from this misconception believe that a constant net force is needed to propel an object at a contant speed. This misconception could arise from the everyday experience of pushing an object across a surface (at a roughly constant speed) which has friction, and not being aware that the friction is acting on the object with an equal amount of force in the opposite direction.

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

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.

Faster moving objects have a larger force acting on them.