9-7 Self Propulsion: Applications of Newton\'s Law and Momentum conservation. Fo
ID: 1459561 • Letter: 9
Question
9-7 Self Propulsion: Applications of Newton's Law and Momentum conservation. For time immemorial people have been cooking up schemes for low energy propulsion. Of course, we believe that whatever is designed better be compatible with Newton's Laws and the Law of Conservation of Momentum (which is actually a consequence of Newton's Second and Third Laws). Several schemes are shown below. Which ones do you think will work? Answer questions detailed in (a) through (d) by referring to the diagrams that follow and do a sketch of each situation to accompany your answer. (a) A lazy fisherman turns on a battery-operated fan and blows air onto the sail of his boat. Will he go anywhere? If he moves, what will his direction be? Explain. (b) A clever child is dangling a large magnet out in front of her wagon. It attracts a smaller magnet that she has attached to the front of her cart. Will she go anywhere? If she moves what will her direction be? Explain. (e) An astronaut is floating in outer space and wants to move backwards. She tosses a ball out in front of her. Will she go anywhere? If she moves. what will her direction be? Explain. (d) A college student on roller blade skates has a carbon dioxide container strapped to her back. The carbon dioxide jets out behind her under pressure. Will she go anywhere? If she moves what will her direction be? Explain.Explanation / Answer
A) Boat propelled by fan: the fisherman will not move, because the action-reaction principle established by the 3rd Newton's Law. This occur by this: in the same way as planes moves by propelled powered engines, the fan will blow the boat in the opposite sense to the air flow expelled of the fan. By the other side, the force acting by the air against the sail is in contrary sense of the blow of fan. Consequently, the couple of forces will null and as a result, the boat doesn't move.
B) Wagon attracted by large magnet: analyzing the system formed by the wagon, the girl and both of magnets (small and large), let's consider the next: the wagon is initially at rest, and it comprises it's own mass, girl's mass and small magnet mass. According to the first Newton's Law, the wagon will stay at rest, unless any external force acts over it, and start the movement. Even with the attraction of the magnets, this force must exceed the needed to start the movement. For this, the large magnet will be attracted to the small, and the wagon will not move.
C) Astronaut floating in outer space: for this case, we need to consider Law of Conservation of Momentum. The astronaut is floating in outer space, and she is moving by any initial condition (i.e. she went out of a spaceship and the wire attached to the ship was broken, etc.). Unless any external force acting over her, or even if she were following a orbit around some planet or The Earth, there is not any force or impulse that she can do that produces some movement different to her condition of "floating" in space.
D) Student in roller blade skates: In this case, the student will move, in contrary sense the blow of carbon dioxide. That occurs, because the force exerted by the gas overcome the force needed to start the movement of the girl. In other words, there is a mass change with time, caused by the dioxide carbon bottle. The variation of mass and velocity with the time cause a change in conservation of momentum, and produces the movement .
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.