Question

1. a fish pushes water backward with its fins. how does this propel the fish forward?

a. the water exerts an internal force on the fish in the opposite direction, pushing the fish forward.
b. the water exerts an external force on the fish in the opposite direction, pushing the fish forward.
c. the water exerts an internal force on the fish in the same direction, pushing the fish forward.
d. the water exerts an external force on the fish in the same direction, pushing the fish forward.

Explanation:

To solve this, we use Newton's Third Law of Motion (action - reaction). When the fish pushes water backward (action), the water exerts an equal and opposite force on the fish. This force is external (as it's between two different objects: fish and water) and in the opposite direction of the water's movement (i.e., forward for the fish).

• Option a: Internal force is incorrect as the force between fish and water is external.
• Option c: Internal force and same direction are wrong.
• Option d: Same direction is wrong.
• Option b: Matches the action - reaction principle, external force and opposite direction (pushing fish forward).

Answer:

b. The water exerts an external force on the fish in the opposite direction, pushing the fish forward.