Question

On a stationary sail boat, air is blown from a fan attached to the boat. The boat will

• A. not move
• B. spin around
• C. more in the direction in which air is blown.
• D. move in the opposite direction to the direction in which air is blow.

Answer 1

The correct option is A

not move

The explanation for the correct option:

(a) The boat will not move: -

1. According to the first law of motion, to change the state of rest or state of motion there must be an external unbalanced force.
2. According to the third law of motion, to each and every action, there is an equal and opposite reaction.
3. The boat and fan are systems. So the forces they exert on each other are internal forces. Both the internal forces act on the boat. So, the net force on the boat is zero.
4. The net force on the boat is zero. So, by the first law of motion, it will continue to remain in a state of rest.

The explanation for the incorrect options:

Since the net force on the boat is zero, the boat will remain at rest thus the option (b), (c) and (d) are incorrect.

Therefore, if the air is blown from a fan attached to the stationary sailboat then the boat will not move. Thus, option (a) is correct.