Blocks with a 'x' force and a 'y' acceleration

In summary: N m=2.8kg ax= 3.8m/s^2Correct. So, do you know how to solve for fx2 now?that's where i got stuck.i was thinking that i had to multiply fx2= (2.8kg)(3.8m/s^2) and that's it.I'm afraid that doesn't make any sense. Just look at the units involved. What are the units of force? What are the units of mass? What are the units of acceleration? Do you see how they can't be multiplied together? What
  • #1
Robertoalva
140
0
1. Two forces are the only forces acting on a 2.8 kg object which moves with an acceleration of 3.8 m/s^2 in the positive y direction. One of the forces acts in the positive x direction and has a magnitude of 6.5 N.What is the magnitude of the other force f2?



Homework Equations


F=ma


The Attempt at a Solution



I suppose that to get the second force i just have to multiply F[SUB/]2[SUB/]=ma=(2.8kg)(3.8m/s^2) right?
 
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  • #2
Robertoalva said:
I suppose that to get the second force i just have to multiply F[SUB/]2[SUB/]=ma=(2.8kg)(3.8m/s^2) right?

No. In the equation F = ma, F is the net force (the vector sum of all of the forces acting on the object). For a problem like this, it will be a good idea to express the second law in component form:

ƩFx = max
ƩFy = may
 
  • #3
Robertoalva said:
Problem statement:

1. Two forces are the only forces acting on a 2.8 kg object which moves with an acceleration of 3.8 m/s^2 in the positive y direction. One of the forces acts in the positive x direction and has a magnitude of 6.5 N.What is the magnitude of the other force f2?

Homework Equations


F=ma

The Attempt at a Solution



I suppose that to get the second force i just have to multiply F2=ma=(2.8kg)(3.8m/s^2) right?
[Took the liberty of fixing up some format errors.]

That gets you almost half way there. :smile: But not all of the way there. :frown:

Is there a non-zero component of the object's acceleration in the x-direction? What does that say about the sum of the forces in the x-direction?

[Edit: Tsny beat me again. Serves me right for typing too slow.]
 
  • #4
so basically, the whole thing is accelerating in a sum vector ? that i have to find with f2=sqrt(fx^2 + fy^2)?
 
  • #5
Robertoalva said:
i have to find with f2=sqrt(fx^2 + fy^2)?

Yes. See if you can find f2x and f2y.
 
  • #6
well, I already have fx and now i have to get fy= m*ay and then i just substitute the values of fx and fy in f2=sqrt(fx^2 + fy^2) am I correct?
 
  • #7
Robertoalva said:
well, I already have fx and now i have to get fy= m*ay and then i just substitute the values of fx and fy in f2=sqrt(fx^2 + fy^2) am I correct?

I think so. Just to make sure you're going through the reasoning correctly, the equation ƩFy = may would be expressed as f1y + f2y = may, right? But then you already know the value of f1y, so you can find f2y. I believe that's how you are thinking, just wanted to make sure.
 
  • #8
no! i had another reasoning. i was going to just get fy= ma=(2.8 kg)(3.8m/s^2) and then because they give me already fx = 6.5 N ia was just going to get the vector sum, F= sqrt(fx^2 + fy^2)
it was very different!
 
  • #9
Robertoalva said:
no! i had another reasoning. i was going to just get fy= ma=(2.8 kg)(3.8m/s^2) and then because they give me already fx = 6.5 N ia was just going to get the vector sum, F= sqrt(fx^2 + fy^2)
it was very different!

Oh, not good. There are two forces acting on the object: f1 and f2. Each force is a vector. You need to find the magnitude of one of those forces, namely |f2| = √(f2x2+ f2y2) .

So you need to find f2x and f2y. You are not given either of those. But you can find them by setting up ƩFx = max and solving for f2x and setting up ƩFy = may and solving for f2y.
 
  • #10
Robertoalva said:
no! i had another reasoning. i was going to just get fy= ma=(2.8 kg)(3.8m/s^2) and then because they give me already fx = 6.5 N ia was just going to get the vector sum, F= sqrt(fx^2 + fy^2)
it was very different!

TSny said:
Oh, not good. There are two forces acting on the object: f1 and f2. Each force is a vector. You need to find the magnitude of one of those forces, namely |f2| = √(f2x2+ f2y2) .

So you need to find f2x and f2y. You are not given either of those. But you can find them by setting up ƩFx = max and solving for f2x and setting up ƩFy = may and solving for f2y.

I think you are both talking about the same thing. TSny's notation is less ambiguous though.
 
  • #11
oh! yes, we're talking about the same thing, but the only thing that i didn't quiet understood in TSny's notations were the f2's. i thought that TSny's was trying to tell me that i had to get 2 forces which were f1 and f2 and each one was fx1=m*ay and f1=m*ax, and for fy2=m*ay and fx2= m*ax. but know i see that he's just telling me that:

|f2| = √(f2x2+ f2y2)

f2x= Fx /m = ax
f2y= Fy=m*ay

right?
 
  • #12
Robertoalva said:
f2x= Fx /m = ax
f2y= Fy=m*ay

right?

I'm afraid that's not right at all. Think about it...How can a force equal an acceleration? They don't even have the same dimensions (units). Also, it's not clear what the symbols Fx and Fy mean here.

Let's take it kind of slowly. Consider the fundamental equation ƩFx = max. Can you write out the left hand side of the equation using one or more of the symbols: f1x, f2x, f1y, and f2y?
 
  • #13
f2x-f1x=m*ax ?
 
  • #14
Robertoalva said:
f2x-f1x=m*ax ?
That's close, but why the minus sign on the left? The notation ƩFx means to add together all of the x-components of all of the forces acting on the object. That gives the total x-component of force acting on the object and it's that total x-component of force that equals max.

So, what should the equation ƩFx = max look like?
 
  • #15
fx1+fx2=m*ax
 
  • #16
Robertoalva said:
fx1+fx2=m*ax

Very good. Now, what is the unkown quantity in this equation for which you want to solve? What are the numerical values of all of the other quantities?
 
  • #17
dude! i already solved this equation ! i just did the following thing:

f2=sqrt((f given)^2 + (mass*acceleration y)^2)

i got it right
 
  • #18
Getting the right answer is one thing, clearly understanding the solution is another. Do you feel that it is all clear now?
 
  • #19
i think that what you were trying to teach me was deriving all the formulas to get what i did right?
 
  • #20
Yes, I just wanted to make sure you understood the thought process.

For example, suppose f1 was still 6.5 N but in a direction of 30o above the positive x-direction. Everything else in the problem is kept the same. Would you still be able to solve for the magnitude of f2? If so, then I think you are understanding it.
 

1. What is the relationship between force and acceleration in blocks with an 'x' force and a 'y' acceleration?

The relationship between force and acceleration is described by Newton's Second Law of Motion, which states that an object's acceleration is directly proportional to the net force acting on it and inversely proportional to its mass. This means that for a constant mass, an increase in force will result in an increase in acceleration.

2. How does the direction of the force affect the acceleration of a block with an 'x' force and a 'y' acceleration?

The direction of the force is an important factor in determining the acceleration of a block. If the force and acceleration are in the same direction, the block will experience a positive acceleration. If the force and acceleration are in opposite directions, the block will experience a negative acceleration, also known as deceleration.

3. Can a block have a larger acceleration with a smaller force?

Yes, a block can have a larger acceleration with a smaller force if the mass of the block is smaller. This is because acceleration is inversely proportional to mass, so a smaller mass will result in a larger acceleration for a given force.

4. How does friction impact the force and acceleration of a block?

Friction is a force that opposes motion and can significantly impact the force and acceleration of a block. If there is friction present, it will act in the opposite direction of the applied force, reducing the overall force and therefore the acceleration of the block.

5. How can the force and acceleration of a block be calculated?

The force and acceleration of a block can be calculated using Newton's Second Law, which states that force (F) is equal to mass (m) times acceleration (a), or F = ma. This equation can be rearranged to solve for any of the variables, depending on the given information.

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