ATTWOOD'S MACHINE (rope + pully)

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Homework Help Overview

The discussion revolves around Attwood's Machine, where two different masses are suspended on either side of a pulley system. The original poster aims to determine the force of gravity acting on the masses, with a specific expectation of arriving at an acceleration of 9.8 m/s². The context includes measurements of distance, time, and initial velocity, with references to Newton's laws of motion.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the application of Newton's second law and the relationship between measured acceleration and gravitational acceleration. There are attempts to calculate net forces acting on the masses and questions about the implications of different mass values on the overall system. Some participants express confusion regarding the wording of the problem and the expected outcomes.

Discussion Status

The discussion is ongoing, with participants providing guidance on identifying forces and applying Newton's second law. There is acknowledgment of the need for clarity regarding the problem's wording and the relationship between the measured acceleration and gravitational acceleration. Some participants are exploring the implications of using specific mass values in their calculations.

Contextual Notes

Participants note potential inaccuracies in the measured time and distance values, which could affect the calculations. There is also mention of the original poster conducting a physical experiment to gather data, which adds a practical dimension to the theoretical discussion.

twenty5
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Homework Statement


Determine the force of gravity acting on the masses (we want to end up with 9.8m/s2---> My situation : A rope with 2 different masses hanging on each side, is held by a pulley. The heavier mass falls towards one end. (teacher said something about the mass having to cancel out afterwards) or so.

Homework Equations


d=v1t +1/2at2
I think we can use Newton's second law, F=ma

t=0.9s
d=0.36m
v1=0m/s

The Attempt at a Solution


I used d=v1t +1/2at2 and got acceleration which came out to be .889m/s2

I was wondering what steps I can take now
 
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How does the measured acceleration relate to the acceleration due to gravity (g)?

You'll need to apply Newton's laws to analyze the system. Apply F = ma to each mass.
 
Doc Al said:
How does the measured acceleration relate to the acceleration due to gravity (g)?

You'll need to apply Newton's laws to analyze the system. Apply F = ma to each mass.

awesome ^^ i just tried that juuust right before you replied haha thanks Now I know I am sort of on the right track^^
 
ok I am stuck again xD
 
Show exactly what you did and where you got stuck.
 
Doc Al said:
Show exactly what you did and where you got stuck.

ok So,
step 1:
d = v1t +1/2at2
got acceleration = .889m/s2

Mass A:

FA=ma
FA=0.889a

Mass B:
FB=ma
FB=0.889a

I got stuck right there, like what can I do with it? can I find net force because If I subtract FA and Fb, it'd be 0N O_O, but since I am 100% sure that the Net force isn't 0, what do I do? because Newtons second law states that, if the object is at rest, or at a constant velocity, the net force is 0. but the mass is acceleration towards the floor =P so it cannot be 0
 
ehhh... anything? I am still stuck there lol...been working on it and still working on it ^^
 
Last edited:
You must first identify the forces acting on each mass, find the net force on each (symbolically), and then apply Newton's 2nd law (∑F = ma) to each. You'll get two equations (one for each mass) which you will combine.
 
I don't think you can finish it without knowing something about the masses.
The wording is inconsistent, too - it asks for a force, then says it should have units of acceleration. Could you check the question again and make sure it has been copied word for word?
 
  • #10
Also:
twenty5 said:
ok So,
step 1:
d = v1t +1/2at2
got acceleration = .889m/s2
This makes sense, assuming you solved for the acceleration correctly.

Mass A:

FA=ma
FA=0.889a

Mass B:
FB=ma
FB=0.889a
But I don't know what you're doing here. Each mass is different, so call them m1 and m2. Your equations will look something like:

∑F(on m1) = m1*a
∑F(on m2) = m2*a

Note that if m1 has an acceleration of a downward, then m2 must have an acceleration of a upward.
 
  • #11
MMMM, i just found out that we can use a value for mass...

m1 = .1kg
m2 = .2kg
and now I need to figure out how to get g = 9.8
 
  • #12
Oh, now you can do it knowing the masses!

Sum of forces = ma, where m is the total mass.
Put in an mg for each force.
 
  • #13
ok I'll try that ^^
 
  • #14
ok I got... for the sum of forces is the following...

FA= mg
FA= .1g N

FB= mg
FB= .2g N

FNET = FB - FA
FNET = .1g N

Fsum of forces = .3g
.1g = .3g?

and now I don't know how this will get me to 9.8 ^^

mmmmmmmmmm

I also tried doing...

Ftotal force = ma, where I subbed in the a that I obtained from before...

0.1g = 0.3*0.889
g = 2.6m/s2...

But If I heard the teacher correctly, I believe I heard I'm supposed to get 9.8 or something lol
 
Last edited:
  • #15
sum of forces = ma
.2g - .1g = .3*0.889
you can easily find the ACCELERATION of gravity.
No, it isn't working out to 9.8 as you would expect . . . on Earth.
Your question says find the FORCE of gravity - not sure what that means in this case since there are 2 different masses so two different forces of gravity. Check the wording again?
 
  • #16
Delphi51 said:
sum of forces = ma
.2g - .1g = .3*0.889
you can easily find the ACCELERATION of gravity.
No, it isn't working out to 9.8 as you would expect . . . on Earth.
Your question says find the FORCE of gravity - not sure what that means in this case since there are 2 different masses so two different forces of gravity. Check the wording again?

sorry, the question just says

Attwood's Machine - Measure Acceleration, calculate g.

I also did the experiment physically too =P

I made a pulley with a rope and a mass on either end. and I just let it drop, timed it, and measured the distance =P
 
  • #17
Are you sure the values of time and distance are accurate? Given those two masses g should be equal to 3a.
 

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