Question

what causes a squid to move forward in jet propulsion?
a the force that the water jet applies back on the squid.
b the sucking of seawater into the squids body.
c the force that the squid applies on the water jet.
d the shooting of seawater out of the squids body.

Explanation:

According to Newton's third law of motion, for every action, there is an equal and opposite reaction. When a squid expels (shoots) water out (action - force applied by squid on water), the water exerts an equal and opposite force (reaction) on the squid. This reaction force (the force that the water jet applies back on the squid) is what causes the squid to move forward.

• Option B (sucking of seawater) is just the preparatory step for jet - propulsion, not the cause of forward motion.
• Option C (force squid applies on water jet) is the action force, but it is the reaction force (on squid) that moves it forward.
• Option D (shooting of seawater) is the action (applying force on water), but again, it is the reaction force (on squid) that leads to forward motion.

Answer:

A. The force that the water jet applies back on the squid.