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8th February 2010, 05:05pm
#1
by Lebeast
Lancaster United States
Member Since: May 2009
Member Points: 620

Consider what happens when you jump up in the air. Which of the followings is the most correct?                                                                                  

A; It is the upward force exerted by the ground that pushes you up, but this force can never exceed your weight.                                                

B; When you jump up the earth exerts a force F1 on you and you exert a force F2 on the earth. You go up because F1 > F2.                      

C;   Since the ground is stationary, it cannot exert the upward force necessary to propel you into the air. Instead, it is the internal forces of your muscles acting on your body itself that propels the body into the air             

D; You are able to spring up because the earth exerts a force upward on you that is stronger than the downward force you exert on the earth.

E; When you push down on the earth with a force greater than your weight, the earth will push back with the same magnitude force and thus propel you into the air.

    Which one is right and why?

8th February 2010, 06:25pm
#2
by Sousuke511
Santo Domingo Dominican Republic
Member Since: Feb 2009
Member Points: 2395

I guess is B, if F2 were greater than F1, you would stand still and kick the earth's butt (im ok at economics, physics... basic school stuff and that was long ago)

8th February 2010, 06:27pm
#3
by flying2828
United States
Member Since: May 2008
Member Points: 460

I think that the answer is E!

Process of elimination:

A is wrong because the force the earth pushes up on you when you are standing still is equal to your weight.  When you push down on the earth, you are adding more force to your original weight.  Therefore, the earth will push back with a force greater than your weight (Newton's Laws..  equal and opposite reaction..).

B is wrong, again, because of Newton's Laws.  Each opposite force is equal.

C is wrong because the ground does exert a force up on you...  I think.

D is wrong because it is a restatemend of B.

E is correct!!!  It is also the opposite of A.

 

I might be wrong!!  I am only four days into Physics...

8th February 2010, 06:30pm
#4
by Sousuke511
Santo Domingo Dominican Republic
Member Since: Feb 2009
Member Points: 2395

What you say about D and B is true, dunno which one is (dont really care as long as i can jump), but the elimination process looks great! hehe

9th February 2010, 08:16pm
#5
by rgrizzard
Austin, TX United States
Member Since: Dec 2007
Member Points: 214

The correct answer is E.  A, B, and D all contradict newton's 3rd law, and C is just total bullshit.

5th March 2010, 10:03pm
#6
by clinttherakam
Konoha Australia
Member Since: Dec 2009
Member Points: 2212

DONT DISS C!!!!!!!!! 

I think its C because it stands for COOL!!!!!Cool

Just kidding its probably E since majority RULES!!!!!!!!!!!!

5th March 2010, 11:48pm
#7
by woodshover
United States
Member Since: Dec 2009
Member Points: 7479

Go with E. For every action there is an equal and opisite action, or something like that. Since the earth is so much bigger than you, it's movement is un detectable.

 

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