Question

Bode made a rocket using an empty plastic bottle and fins made out of cardboard. After partially filling the bottle with water, he pumps air into the bottle using a pump attached to the rocket with plastic tubes. When the pressure in the bottle becomes high enough, the water gushes out and launches the rocket into the air, as shown in the diagram below.



Image modified courtesy of NASA


How does the force that causes the water to leave the rocket compare to the force that causes the rocket to launch?
A.
They are unequal and act in the same direction.
B.
They are unequal and act in opposite directions.
C.
They are equal and act in the same direction.
D.
They are equal and act in opposite directions.

Answer 1

D.

By Newton's third law the force the rocket (bottle/nozzle) exerts on the water is equal in magnitude and opposite in direction to the force the water exerts on the rocket. The internal pressure pushes water out backward; the expelled water pushes the rocket forward with the same magnitude of force.