|
About Newton's Third Law... *plz help my homework*
|
|
Can anybody help me by answering these questions? i really need them today... although i already had the answers for number 2 & 3 *that i got from google :p* but if u hv another ans, ^^ u may write them... heheheheheheheheh..... 1. Why is it important that an aeroplane's wings be designed so that it deflects on coming air downward?? 2. Would it be a good idea to jump from a rowboat to a dock that seems within jumping distance? Explain. 3. If we throw a ball horizontally while standing on roller skates, we roll backward with a momentum that matches that of the ball. Will we roll backward if we go through the motion of throwing the ball without letting go of it? Explain.
幸ã›ã¯ã©ã“？
神様ã€ã‚ãŸã—ã«å¹¸ã›ã‚’ã‚ã’ã¦ãã‚Œã¦ãã ã•ã„。。
|
|
Re: About Newton's Third Law... *plz help my homework*
Link |
by
 
on 2007-02-15 09:54:26 |
|
will try to give a suggestion.. 1. So that the aeroplane remains in equilibrium when flying in the air..u know the way when u place a book on the table, the table would exert an equal and opposite reaction force on the book ( which is pulled downwards by gravity)--this way the book remains stationary one of the conditions of equilibrium is that there should be no resultant force..there's no force from above the plane therefore you cannot hav a force from downwards for the plane to fly with constant speed in a straight line 2. seems to be a no but i can't be sure why..when u jump a across, you exert a force on the boat..therefore it also exerts a reaction force on your body, pushing you away from it..this is just an idea but what if some energy is absorbed by the water below? (well if itz me i'd probably just jump anyway..if im confident enough lol) 3. No ? I don't think it will coz if you're still holding the ball, the pull of gravity on the ball(the weight of it) would sorta keep you in the upright & steady position.. hope it helped...im not sure about 2 & 3 though..gd luck on finding the answers  |
|
Re: About Newton's Third Law... *plz help my homework*
Link |
by none123456
on 2007-02-16 09:27:20
|
|
1. For every force, there is an equal force, but opposite in direction. Based on your questions, I'm GUESSING this is the Third Newton Law. For the airplane (actually a kite would be a better example IMO), the wings are tilted because the tilt forces air to be pushed down, as the wings guide it. Think of a fan, where the tilt on the fan allows it to blow air. Because of this tilt, as the air gets pushed down, the Law states that there should be an equal force in the opposite direction, and thus lift is created as the airplane is pushed UP from the air being pushed DOWN. 2.Depends on a multitude of factors. You could be "smart" and say the rowboat is flat enough and is on flat ground when you jump :p. Assuming the rowboat is bobbing in the water, I would say no. This is simply because again, while it seems that on flat ground you will be able to make it (simply because the earth has so much mass that any force against it would move it minutely), the rowboat would be affected much more by any force. Thus, you would propel yourself with less force, most likely not enough to jump to shore. 3. Depends where you finish the "throw" with the ball. As you are throwing the ball, essentially you are applying a force to the ball, and you roll backwards. If you stop the ball in front of you (fully extended arm), you exert the same amount of force to stop the ball, and you stop rolling. HOWEVER, since you did work to the ball, there has to be work done to you, so you would have moved slightly in the opposite direction. Also, if you return the ball back to it's original position at the end of the throw, you make the work 0 as well, and thus really no change. This is assuming that there is frictionless environment caused by roller blades (impossible!) I hope that helps, and that I'm not too late. |
|
Re: About Newton's Third Law... *plz help my homework*
Link |
by MiCHiYo μ
on 2007-02-16 09:39:13
|
|
i think i can answer number one: so that there is lift underneath the wings in order to lift the entire contraption. it is designed in a tear-drop shape in order to allow the air to pass underneath it in straightly, whilst above it is curved downwards to allow a push down. the shape also lessens the drag created by the solid material going through gas. (note that not all my terms are the terms used... some of the terms such as "push down" are created by moi. XD) err... seeing number two, here's my answer: no, because when you jump off, you exert force on the boat, allowing it to move backwards, making the distance bigger. therefore, when you actually get off the boat, the distance have changed already, and you will fall into the water. and number three? ahhhhh~ i don't inderstnad it much. do you mean you will "pretend" to throw the ball but not let go and if there is the same momentum as actually letting it go? -michiyo- 
 beware. the QueeN oF SiGGieS is here. kill that mr. scrolly or your siggy goes BAI BAI. it's solidarity month! let's be united! +[-- GeNDouNiaNS: i am half-back! visit my blog by clicking on the siggie banner! updated: 12.07.07 --]+
~*..:: i'm never going to give up... if i do, then it wasn't worth trying. ::..*~
|
|
Re: About Newton's Third Law... *plz help my homework*
Link |
by
on 2007-02-28 20:10:28 |
3. no. not on a frictionless surface. as we wind up and fake-pitch the ball, our center of mass moves, and so does the point of contact with the ground (skates). at the end of the experiment, if we move out center of mass back to the original position, conservation of momentum requires that our skates will be on the same point on the ground, too. 
|