Work & Tension Homework: Find W & Delta K.E.

[Gear2d]

Homework Statement

There is a block with a mass of 4kg attached to a rope where tension is point upwards. The block is lowered by the rope, and the tension is 35N. If block is lowered 10m:

A) What is work done by the rope?
B) What is delta K.E.?

Homework Equations

W = mgh
W = Fd

The Attempt at a Solution

A) W = Fd = -350J

I am having a hard time with the concept as to why the block does not affect the work on the rope. Also, how is the block losing energy (indicated by the negative sign in the solution)?

B) Can I solve it this way:

Fd = delta U + delta K

(35)(10) = (4)(10)(10) + delta K

-50J = delta K

 

[alphysicist]

Homework Statement

There is a block with a mass of 4kg attached to a rope where tension is point upwards. The block is lowered by the rope, and the tension is 35N. If block is lowered 10m:

A) What is work done by the rope?
B) What is delta K.E.?

Homework Equations

W = mgh
W = Fd

You're missing a trig factor here (which gives you the minus sign in part a).

The Attempt at a Solution

A) W = Fd = -350J

I am having a hard time with the concept as to why the block does not affect the work on the rope. Also, how is the block losing energy (indicated by the negative sign in the solution)?

If you compare a block being lowered by this rope to a block that is just dropped 10m, the one that is dropped has more energy after dropping 10m.

B) Can I solve it this way:

Fd = delta U + delta K

(35)(10) = (4)(10)(10) + delta K

You have some sign errors here. You had already found in part a that the work was -350J. For the delta U term, what is delta h?