# Homework Help: Awesome pulley problem

1. Aug 29, 2007

### a_d777

Awesome pulley problem!!!

Hey, i just came across this pulley problem and thought it was easy to solve....on solving, my answers were not matching....!

Check the attachment...

There is a single string. Ignore the friction.
The mass of the pulleys A, B & C is 1 Kg each.
*ignore the dirty, bad diagram...what else can i do in windows!!!???*

also post the method of doing...

correct options are a,b & d...

#### Attached Files:

• ###### phy.JPG
File size:
17.7 KB
Views:
117
2. Aug 29, 2007

### Danger

No fair! Misleading title! I'm going to complain to the Mentors!
I came here expecting something about a chicken cannon. :grumpy:

Seriously, though, welcome to PF. Nothing can be done until your attachment is approved.

3. Aug 29, 2007

### HallsofIvy

Your diagram is excellent- just enlarge it. Note that we do require that you show what you have tried yourself and you must try. To get you started, I would recommend you lable the ropes between pulleys (and the forces for each), say x,y,z,u,v,w. I count 6such ropes and so 6 such forces.

4. Aug 29, 2007

### Danger

Correction. Nothing can be done by non-Mentors, who can't see the attachments until they're approved. :tongue:

5. Aug 29, 2007

### a_d777

hm...

ok, but...
hm...
well, i cant work on my PC so well ...
i mean i cant do high-end editing...Bad in computers....!
i cant even scan the page of my notebook because i dont have a scanner!!!

well, i will surely post what ive tried...veryy soon...!
and, sorry....
its pulleY...
not pulleT
!!!

6. Aug 29, 2007

### Danger

.

7. Aug 29, 2007

### BlackWyvern

Is C fixed?

Have a think as to which are fixed, and (for the start) draw arrows on the diagram indicating which way the string will go.

8. Aug 29, 2007

### DaveC426913

Yeah, you beat me to it.

9. Aug 29, 2007

### chroot

Staff Emeritus
s/pullet/pulley/

- Warren

10. Aug 29, 2007

### pardesi

i really $$don't$$ want to sound stupid but please do attach some points to the cieling(if any) otherwise the system will fall don due to gravity(if any )

anyways just use the fact that in a closed rigid system the tension(internal force) does no work.
since tension on each pulley is known spped hence accelaration of each pulley is known

11. Aug 29, 2007

### rootX

There's an easy way for solving pulley problems, but I really don't know how to use that method.

make an equation using all ropes distances(find relationships between them), and differentiate them.
anyone knows that method?

12. Aug 29, 2007

### pardesi

yes the constrain t method but that's just mathematical representation of what u think intutively
for example consider the standard pulley problem of two masses say $$m_{1}$$ and $$m_{2}$$ hanging on two ends.
now say one get's down by $$x$$ other by $$y$$ then since rope length is constsnt we have
$$x+y=0$$
differentiating
$$\frac{dx}{dt} + \frac{dy}{dt}=0$$
thus $$v_{m_{1}}=-v_{m_{2}}$$
differentiating again
$$a_{m_{1}}=-a_{m_{2}}$$

13. Aug 29, 2007

### rootX

I can't do that with more than two pulleys ><

14. Aug 29, 2007

### Danger

You rat! Now my post just looks stupid.
I'm glad that Dave was a witness to the original title. :tongue:

15. Aug 30, 2007

### pardesi

what is that u couldn't solve

16. Aug 30, 2007

### kaisxuans

hey, isn't there things like photoshop and paint? they are good programs that can help you to edit your pictures. try them! =)

17. Aug 31, 2007

### a_d777

Um...correction...!

sorry for the wrong image...well, not wrong...but incomplete...!
The motion of pulleys or strings is not mentioned in the question...

#### Attached Files:

• ###### phy.JPG
File size:
17.7 KB
Views:
82
Last edited: Aug 31, 2007