Double Pulley Mechanics Problem

In summary, the tension on the cable has to be equal to the downward force from the crate and pulley 2 in order to slowly raise the crate.
  • #1
MissBisson
24
0

Homework Statement


it is a double pulley problem, mass of pulley 1 is 4.1kg, mass of pulley 2 is 6.9kg and mass of crate is 57.2kg.
both pulleys are frictionless. the angle at which the rope is pulled is 45deg. What is the minimum tension with which the operator must pull on the cable (negligible mass) in order to slowly raise the crate?

Homework Equations


i was wondering if this was a torque problem of simply a one dimensional problem involving pulleys? also do we need to use Newtons second law?

The Attempt at a Solution


I tried ignoring the masses of the pulleys since we have not yet learn torque but the answer was wrong. however the radius of the pulleys are not given so i am not sure i can use torque for this problem?

Here is the image : https://s.yimg.com/hd/answers/i/ff7b49a654fb4768a4d9902f8dc5ac60_A.png?a=answers&mr=0&x=1413224583&s=0388b130543c86fed3259f977c0872ce [Broken]
 
Last edited by a moderator:
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  • #2
MissBisson said:

Homework Statement


it is a double pulley problem, mass of pulley 1 is 4.1kg, mass of pulley 2 is 6.9kg and mass of crate is 57.2kg.
both pulleys are frictionless. the angle at which the rope is pulled is 45deg. What is the minimum tension with which the operator must pull on the cable (negligible mass) in order to slowly raise the crate?

Homework Equations


i was wondering if this was a torque problem of simply a one dimensional problem involving pulleys? also do we need to use Newtons second law?

The Attempt at a Solution


I tried ignoring the masses of the pulleys since we have not yet learn torque but the answer was wrong. however the radius of the pulleys are not given so i am not sure i can use torque for this problem?

Here is the image : https://s.yimg.com/hd/answers/i/ff7b49a654fb4768a4d9902f8dc5ac60_A.png?a=answers&mr=0&x=1413224583&s=0388b130543c86fed3259f977c0872ce [Broken]
I believe you can ignore pulley 1, as it is not being lifted, but you have to include pulley 2. Pulling on the cable lifts both the crate and pulley 2. The vertical component of the tension will be equal in magnitude to the downward force that comes from the crate and pulley 2. You need to figure out what the tension T is.

BTW, this is not an advanced physics problem, so I moved it to the Intro Physics section.
 
Last edited by a moderator:
  • #3
No need for torques, just forces is enough.
Make a drawing with the forces working on the masses. Which ones have to be dealt with by the rope ?
 

1. What is a double pulley mechanics problem?

A double pulley mechanics problem is a type of physics problem that involves using double pulleys to determine the mechanical advantage and effort required to lift or move an object. It requires an understanding of the principles of pulleys, forces, and mechanical advantage.

2. How do I solve a double pulley mechanics problem?

To solve a double pulley mechanics problem, you need to first identify the given information such as the weight of the object, the number of pulleys, and the force applied. Then, you can use the formula MA = load/effort to calculate the mechanical advantage. Finally, use the formula load = MA * effort to determine the amount of weight that can be lifted or moved.

3. What is the mechanical advantage of a double pulley system?

The mechanical advantage of a double pulley system is equal to the number of supporting ropes or strands. In other words, if a double pulley system has two supporting ropes, it will have a mechanical advantage of 2. This means that the effort required to lift an object will be half of the weight of the object.

4. Can a double pulley system have a mechanical advantage greater than 2?

Yes, a double pulley system can have a mechanical advantage greater than 2. This can be achieved by adding more pulleys to the system. Each additional pulley will increase the mechanical advantage by 1, so a system with 3 pulleys will have a mechanical advantage of 3.

5. Are there any real-life applications of double pulley mechanics problems?

Yes, there are many real-life applications of double pulley mechanics problems. For example, cranes and elevators use double pulley systems to lift heavy objects. Sailboats also use double pulleys to raise and lower sails. Additionally, exercise machines such as weightlifting machines and rowing machines use double pulleys to provide resistance.

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