Physics question regarding tension?

Question

I'm having trouble understanding the concepts of tension in this problem. Two 1.6kg blocks are connected by a rope. A second rope hangs beneath the lower block. (The diagram is vertical - one block with another block below connected by a rope and that block with a rope beneath it). Both ropes have a mass of 250g. The entire assembly is accelerated upward at 4.0m/s^2 by force F. What is F? What is the tension at the top end of the rope connecting the two blocks? at the bottom end? What is the tension at the top end of the rope beneath the second block?

Answer 1

You have good intuition. The problem as stated is not complete enough to answer.

For the first part, net force = mass x net acceleration.

mass = mass of blocks + mass of ropes
mass of blocks = 2 x 1.6kg
mass of ropes = 2 x 0.25kg
net acceleration = 4.0 ms/s^2

So you can compute the net force on the assembly. But the use of the words "hangs" and "upward" suggest you are in a gravitational field. If so, how strong is it?

The net force is the sum of the forces so if we have:

net force = F + gravitational force

we need to know the gravitational force to compute F. And it will be different on the surface of the Earth and the surface of the Moon, etc.

As for the tension, the question becomes how is the force F applied?

If the force is applied entirely to the top block, then the tension at any point along any of the ropes is just the force required to accelerate the mass below that point.

For example, the tension at the top of the bottom rope only has to accelerate the 250 gram mass of the bottom rope; the tension at the top of the top rope has to accelerate the bottom block and the two ropes, etc.

However, suppose the force is not applied entirely to the top block. For example, suppose there was a very heavy mass (a small black hole?) firmly fixed above the assembly and that the assembly was accelerating upward because of the gravitational attraction of that mass. Then the gravitational attraction of that mass would be distributed over the entire assembly and the tension on the ropes would be correspondingly lower.

(By analogy, if you are lifting a 100 pound box by pulling up on a rope, the tension in the rope is going to be a lot higher than if, while you are pulling on the rope, someone else is helping by pulling up on the side of the box, even though the total force applied to the box remains the same.)

Answer 2

It is in each instances if there is not any side of the rope that movements. Given that you're pulling in opposition to a 2 hundred 12 months historical healty alrighttree and now not a ninety eight pound sappling weakling so that you could talk, then you definately and your pal can pull in opposition to the tree and it's going to now not supply in any respect. In addition it's going to pull again with an identical anxiety. Now if you're speaking approximately a pal, if you're identical in all approaches and the rope does now not transfer then the reply is the equal as the only above. If your pal isn't as strong as you're and the rope offers a bit of then the anxiety is lower than with the alrighttree. Motion implies much less. Hope it is transparent ample.