Pulley Questions: 15kg, 12kg, Fnet, ma, Fg, mg

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In summary, two weights of 15kg and 12kg are attached to a frictionless pulley in opposite directions. Using the equations Fnet=ma and Fg=mg, the acceleration of the masses is found to be 1.1m/s squared. To find the tension in the rope connecting the masses, the resultant force on either mass is considered, leading to the equation ma=T-mg. Simplifying this equation using the value for the acceleration found earlier, the tension is solved to be 130 Newtons.
  • #1
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Homework Statement



Two weights are attached to a frictionless pulley. 15kg and 12kg each in opposite directions
a) find the acceleration of the masses
b) the tension in the rope connecting the masses

Homework Equations


Fnet=ma
Fg=mg


The Attempt at a Solution



I have found the the answer a) but can't figure out how to find b)
 
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  • #2
magico24 said:

Homework Statement



Two weights are attached to a frictionless pulley. 15kg and 12kg each in opposite directions
a) find the acceleration of the masses
b) the tension in the rope connecting the masses

Homework Equations


Fnet=ma
Fg=mg


The Attempt at a Solution



I have found the the answer a) but can't figure out how to find b)

How did you find part a?

I would like to know how exactly you did it as that might help for part b
 
  • #3
I multiplied gravity times both weight fg=mg, fg=15(9.80) and fg=12(9.80) giving me 147 newtows and 117.6 Newtons than i did Fnet=ma Fnet=147n-117.6n Fnet=29.4 than i did 29.4divided by 27 giving me 1.088889 and i rounded that too 1.1m/s squared. which was the right answer in my answer key
 
  • #4
ok well if that is the answer for a)

There are only two forces acting on either mass, its weight and the tension. What would be the resultant force on either one? (and you have got the resultant acceleration from part a)
 
  • #5
the answer the teacher gives is 130 Newtons. your reply really does not make a whole lot of sense to me.
 
  • #6
i just want to know how he gets this answer. The steps he does
 
  • #7
The 15kg mass has a force of 147 Newtons downwards. I am just confused on the tension of the rope is it something i am just not seeing but i already have the answer to or is is something i need to solve for now using a different equation?
 
  • #8
Well if you considered the forces acting on the 15kg weight. The weight moves down right? So the resultant is down. Tension (T) acts up..weight acts down.

making ma=T-mg (m=15,g=9.8) and you found a.
 
  • #9
The entire thing can be simplified by leaving gravity equal to g. This would make your equations for a the following
15g-t=15a
t-12g=12a (sim equation)
----------
3g=27a
so

3g 1g
-- = a ---
27 or 9

Having found a you can simply sub it into an original equation i.e.
15g-T=15g
---
9


and solve to find T
 

1. What is a pulley and how does it work?

A pulley is a simple machine that is used to lift or move heavy objects. It consists of a wheel with a groove along its circumference and a rope or belt that runs through the groove. By pulling on one end of the rope, the object attached to the other end can be lifted or moved.

2. What does the weight of an object have to do with pulleys?

The weight of an object is important in determining the amount of force needed to lift or move it using a pulley. The greater the weight of the object, the more force is needed to overcome its weight and move it.

3. How do you calculate the net force on an object on a pulley system?

The net force on an object in a pulley system can be calculated by subtracting the weight of the object (Fg or mg) from the applied force (Fnet). The remaining force is the net force acting on the object.

4. What is the relationship between mass and acceleration in a pulley system?

According to Newton's second law of motion, the force applied to an object (Fnet) is equal to the mass of the object (m) multiplied by its acceleration (a). In a pulley system, the mass of the objects on each side of the pulley are equal, so their accelerations will also be equal.

5. How do you calculate the mechanical advantage of a pulley system?

The mechanical advantage of a pulley system can be calculated by dividing the weight of the object being lifted (Fg or mg) by the force applied to the rope (Fnet). This will give you the number of times the force is multiplied by the pulley system to lift the object.

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