Finding net force or acceleration given 2 masses

  • Thread starter BSY
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  • #1
BSY
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Homework Statement


Imagine you put 10 weights of 100grams on wheels. You attach this "car" to a pulley that hangs over a ledge. You take 1 weight of 100grams off the "car" attach it to the hanging edge of the pulley. The car propels forward what was the acceleration of car and/or net force.

Homework Equations


acceleration=Fnet/mass
 

Answers and Replies

  • #2
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What's your attempt at a solution?
 
  • #3
BSY
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I tried using acceleration as the acceleration of gravity to find fnet but the 2 different masses is really throwing me off.
 
  • #4
BSY
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I forgot to mention that the wheels are "massless" so by removing 1 weight and attaching it to the pulley, the car system is now 900g, and there is 100g on the pulley. No matter what the total mass of the entire system stays the same.
 
  • #5
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What is the force acting on the car?
 
  • #6
BSY
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What is the force acting on the car?
That's what I'm trying to find out. I drew an image of the situation.
 

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  • #7
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Don't worry about what's happening anywhere else. Focus only on the car and draw all of the forces acting on the car.
 
  • #8
BSY
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The only force on the car is the 100g weight + gravity acting on the weight. The car is only moving because of that weight. Is Fapp + Fg in the same direction?
 
  • #9
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The only force on the car is the 100g weight + gravity acting on the weight

What exactly do you mean by this?
I see what you're getting at, but you need to be a bit more clear. You're right: there is one force acting on the car. That force is the tension in the rope. Now what is the tension in the rope?
 
  • #10
BSY
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Okay, I think I'm getting it. I would use the equation g=Fg/m. Since in this situation tension force and gravitation would be the same. It could be written as a=Ft/m. I am unsure what I would put in as mass in that equation, a would be equal to 9.81m/s2, which I am now sure of.
 
  • #11
BSY
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Actually, I am not sure if it is 9.81, because of the resistance in acceleration the car provides. But I do believe I will use acceleration of gravity in part of the process.
 
  • #12
BSY
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To find tention force, would I use (0.8kg)(9.81m/s2). Since one mass is on the pulley? Finding what to substitute for mass is my main problem here.
 
  • #13
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Let's approach it this way: you've got two unknowns--the tension and the acceleration. That means you'll need two equations to find them. Write out the equations for the net force on each mass.
 
  • #14
BSY
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Okay. I attached an image of how I think I find Fnet. Only problem with this is that acceleration is always = 9.81m/s2.
 

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