Question

force and motion end - of - unit assessment (continued)

1. at dinner, hans passed the salt shaker to his sister jessica by sliding it across the wooden table. the salt shaker gradually slowed down and stopped after moving 12 centimeters.

why did the salt shaker stop moving?
a. the salt shaker ran out of force.
b. the table exerts a force that is opposite to the salt shakers motion.
c. the table absorbs force from the salt shaker.
d. all objects stop moving because their natural state is to be still.

Explanation:

According to Newton's first law of motion, an object in motion will stay in motion unless acted upon by an external force. In this case, the salt shaker stops moving because of the frictional force. Friction is a force that opposes the motion of an object. When the salt shaker is sliding on the wooden table, the table exerts a frictional force on the salt shaker in the opposite direction of its motion. This frictional force gradually slows down the salt shaker until it stops.

• Option a is incorrect because force is not something that an object "runs out of." Force is an interaction between objects.
• Option c is incorrect because the table does not "absorb" force in the way described. It exerts a frictional force.
• Option d is incorrect because it goes against Newton's first law. Objects do not have a "natural state" of being still; they remain in their state of motion (or rest) unless acted upon by an external force.

Answer:

B. The table exerts a force that is opposite to the salt shaker’s motion.