2 equal masses raised on pulley at constant velocity, what is the force ?

In summary, the conversation discusses the force acting on two equal masses being raised up a pulley at a constant velocity. It is stated that massB has a velocity twice as fast as massA, leading to confusion about how this is possible without an additional force. It is then clarified that pulleys allow for different speeds to be achieved by applying the same unbalanced force for different amounts of time. The conversation concludes by acknowledging that the given information was incomplete and that understanding can make previous confusion seem silly.
  • #1
mldavis086
10
0

Homework Statement



2 equal masses (massA, massB) are raised up a pulley, at a constant velocity. massB has a velocity twice as fast as massA. What is the force acting on these 2 masses?

Homework Equations





The Attempt at a Solution



If it is a constant velocity, the upwards force must be equal to mg correct? So Fa=mg, Fb=mg. But if this is the case, how is it possible massB moves twice as fast as massA without an additional force acting on it?

I am confused, can anyone out there help me please?
 
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  • #2
Hint: what do pulleys do? What are they for?

Note: a net zero force is needed to move at any constant speed - so two equal masses can have the same applied force and yet move at different constant speeds. You get different speeds by applying, for eg., the same unbalanced force for different amounts of time. But I don't think they are talking about the force on the mass - but the force applied to the end of the rope.

(However: I don't think all that is all the information you are given.)
 
  • #3
No it is not all the given info. It was a power question but I got it figured out. I was just confused about the part where it could be any speed. But now it seems like a silly question now that I understand. Thanks though!
 
  • #4
Once you understand something, earlier confusion often appears silly.
We are all wise in hindsight ;)
Cheers.
 
  • #5


I would first clarify the setup of the experiment. Are the masses connected by a rope passing over the pulley, or are they attached to opposite ends of the pulley? This will affect the tension in the rope and the forces acting on the masses.

Assuming the masses are connected by a rope, the tension in the rope must be equal at all points. This means that the force pulling up on massB must be twice the force pulling up on massA, in order for massB to move at twice the velocity of massA. This is because the tension in the rope is the force that is causing the masses to move.

So, the force acting on massA would be half of the weight of massA (F=mg/2), and the force acting on massB would be equal to the weight of massB (F=mg). This would result in both masses moving at a constant velocity, with massB moving twice as fast as massA.

It is important to note that the upward force on massA is not equal to the weight of massA, as there is an additional force (the tension in the rope) acting on it. In this scenario, the force on massA is equal to the weight of massA minus the tension in the rope.

In summary, the force acting on the 2 masses in this scenario is the weight of massA minus the tension in the rope (F=mg-T) for massA, and the weight of massB (F=mg) for massB.
 

1. What is the formula for calculating force in this scenario?

The formula for calculating force in this scenario is F = m x a, where F represents force, m represents mass, and a represents acceleration.

2. Is the force the same on both masses?

Yes, the force is equal on both masses because they are connected by a pulley and moving at a constant velocity.

3. How does the force change if the masses are not equal?

If the masses are not equal, the force will be greater on the heavier mass and less on the lighter mass. This is due to the principle of Newton's Third Law of Motion, which states that for every action, there is an equal and opposite reaction.

4. Does the force change if the velocity changes?

Yes, if the velocity changes, the force will also change. This is because force is directly proportional to acceleration, which is a component of velocity.

5. What other factors can affect the force in this scenario?

Aside from mass and velocity, other factors that can affect the force in this scenario include friction, air resistance, and the angle of the pulley. These factors can either increase or decrease the force acting on the masses.

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