# Conservation of momentum in pulley

• jd12345
In summary, when two blocks of mass m are connected by a light string passing over a pulley, pushing one block downwards with force F will result in the other block moving upwards with the same speed v. However, momentum is only conserved for the whole system, not its individual pieces. The force applied also affects the pulley and the Earth, resulting in a net change of zero momentum for the entire system.
jd12345
Two blocks of mass m connected by a light string passing over a pulley.
Say, one of the blocks is pushed downwards with a force F and it attains velocity v.So the other block moves upwards with the same speed v right?

Total moementum = mv - mv = 0( because one is moving upwards and other downwards so opposite directions of velocity)

So we applied force but still no momentum change??
Where did i go wrong??

Momentum is a vector, for one thing. Direction counts. And do not ignore the external force of the pulley's axle on the system.

jd12345 said:
Two blocks of mass m connected by a light string passing over a pulley.
Say, one of the blocks is pushed downwards with a force F and it attains velocity v.So the other block moves upwards with the same speed v right?

Total moementum = mv - mv = 0( because one is moving upwards and other downwards so opposite directions of velocity)

So we applied force but still no momentum change??
Where did i go wrong??

When you push on the one mass, you are also pushing on the pulley, and the pulley is connected to the earth, so you are pushing on the Earth too. Momentum is only conserved for the whole system, not its pieces. The pieces are the two masses, you, and the pulley-earth (they are rigidly connected). The force that you apply adds momentum to the earth, not to the masses.

When you push on the mass, it pushes back (Newton's law). That means you have momentum up, which matches the down momentum of the pulley-earth. Total momentum is still zero. When you stop applying the force, gravity pulls you and the pulley Earth together, and both stop. The masses are moving with zero momentum, you and the pulley Earth are motionless, and again, total momentum is zero.

## 1. What is conservation of momentum in pulley?

The conservation of momentum in pulley is a fundamental principle in physics that states that the total momentum of a system remains constant as long as there are no external forces acting on the system. In a pulley system, this means that the total momentum of the objects on either side of the pulley will remain the same as they move.

## 2. How does conservation of momentum apply to pulley systems?

In a pulley system, the conservation of momentum applies because the total momentum of the objects on either side of the pulley must remain the same as they move. This is because the pulley itself does not contribute any external forces to the system, so the total momentum of the system must remain constant.

## 3. What happens to the momentum of the objects in a pulley system?

The momentum of the objects in a pulley system remains constant as they move. This means that if one object gains momentum, the other object must lose an equal amount of momentum in order to maintain the total momentum of the system. This exchange of momentum allows the objects to move in opposite directions while still obeying the principle of conservation of momentum.

## 4. How does the mass of the objects affect conservation of momentum in pulley?

The mass of the objects in a pulley system does not affect the conservation of momentum. This is because the principle of conservation of momentum states that the total momentum of the system remains constant, regardless of the individual masses of the objects. However, the mass of the objects can affect the speed at which they move, as objects with greater mass will have a slower speed compared to objects with less mass.

## 5. Are there any real-life applications of conservation of momentum in pulley?

Yes, there are many real-life applications of conservation of momentum in pulley systems. One example is in elevators, where pulley systems are used to lift and lower the elevator car. The conservation of momentum allows for the car to move up and down smoothly without the need for a motor. Another example is in rock climbing, where pulley systems are used to reduce the amount of force needed to lift a climber up the rock face. This allows for easier and safer climbing.

Replies
31
Views
4K
Replies
30
Views
2K
Replies
12
Views
1K
Replies
16
Views
2K
Replies
53
Views
3K
Replies
4
Views
2K
Replies
6
Views
1K
Replies
2
Views
1K
Replies
4
Views
1K
Replies
27
Views
2K