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Newton second law involving a gallon of water

  • Thread starter kadoma
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  • #1
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Homework Statement


a box filled of water is over at the beginning of a incline plane of 30 degree, it has a mass of 1 kg,from the bottom of the plane to the top is 10m, the gallon is pushed with a force of 10N to the top, and the gallon is leaking 0.01kg per second

what is the final velocity?

Homework Equations



f=ma

The Attempt at a Solution


analyzing this problem each since the force doesnt change, the mass decrease each second so the acceleration increase each second. i really dont know how to solve this problem when involving a gallon of water leaking.
 
Last edited:

Answers and Replies

  • #2
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Only when the mass remains constant does Newton's Second Law of motion reduce to
[tex]\vec{F}=m\vec{a}[/tex]
When dealing with variable mass, use
[tex]\vec{F}=\frac{d}{dt}(m\vec{v})[/tex]
 
  • #3
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Last edited:
  • #4
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Only when the mass remains constant does Newton's Second Law of motion reduce to
[tex]\vec{F}=m\vec{a}[/tex]
When dealing with variable mass, use
[tex]\vec{F}=\frac{d}{dt}(m\vec{v})[/tex]
so it means the mass is constant, it only changes the velocity
 
  • #5
798
1
No, the mass is not constant. It is changing with time. Also, did you copy the question down fully, and properly?
 
  • #6
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well if you dont understand my question u can ask me
 
  • #7
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as far i understand time is changing as well as mass and velocity
 
  • #8
Ray Vickson
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Only when the mass remains constant does Newton's Second Law of motion reduce to
[tex]\vec{F}=m\vec{a}[/tex]
When dealing with variable mass, use
[tex]\vec{F}=\frac{d}{dt}(m\vec{v})[/tex]
This equation is known to be incorrect in general, although it is true in some cases. Correct classical variable-mass equations of motion were finally well established in the 1990s! Before that, many incorrect results appeared in the published literature. Google 'variable-mass dynamics' for relevant papers.

RGV
 
  • #9
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so... this is harder now, can u help me?
 
  • #10
PeterO
Homework Helper
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Homework Statement


a gallon of water is over at the beginning of a incline plane of 30 degree, it has a mass of 1 kg,from the bottom of the plane to the top is 10m, the gallon is pushed with a force of 10N to the top, and the gallon is leaking 0.01kg per second

what is the final velocity?

Homework Equations



f=ma

The Attempt at a Solution


analyzing this problem each since the force doesnt change, the mass decrease each second so the acceleration increase each second. i really dont know how to solve this problem when involving a gallon of water leaking.
A couple of questions:

Is this a gallon of water or a kilgram of water? A litre of water has a mass of 1 kg.
If this is a gallon, is this a US gallon [8 lb] or an imperial gallon [10 lb],

EDIT: I ask about which gallon as I don't know where you are posting from.
 
Last edited:
  • #11
798
1
This equation is known to be incorrect in general, although it is true in some cases. Correct classical variable-mass equations of motion were finally well established in the 1990s! Before that, many incorrect results appeared in the published literature. Google 'variable-mass dynamics' for relevant papers.

RGV
Interesting to know.. Especially considering this was in my Calculus textbook from January 2009.
 
  • #12
8
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A couple of questions:

Is this a gallon of water or a kilgram of water? A litre of water has a mass of 1 kg.
If this is a gallon, is this a US gallon [8 lb] or an imperial gallon [10 lb],

EDIT: I ask about which gallon as I don't know where you are posting from.
actually is not really a gallon of water....is just a box or tank filled with water which leak every second.
 
  • #13
322
0
A couple of questions:

Is this a gallon of water or a kilgram of water? A litre of water has a mass of 1 kg.
If this is a gallon, is this a US gallon [8 lb] or an imperial gallon [10 lb],

EDIT: I ask about which gallon as I don't know where you are posting from.
i'm pretty sure that the volume isn't important just the change in mass
 
  • #14
PeterO
Homework Helper
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actually is not really a gallon of water....is just a box or tank filled with water which leak every second.
If the box was not leaking, it would take only about 2 seconds to reach the top, arriving with a velocity of about 10 m/s.

In two seconds, the mass will have reduced from 1.00 kg to 0.98 kg - a very small change, so the final velocity won't be much bigger.
Since data was given to one specific figure only, the answer should be 1 x 101 regardless.
 
  • #15
8
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i already solved it
 

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