# Homework Help: Internal Forces (Engineering Mechanics)

1. Oct 29, 2005

### physicsss

problem says knowing radius of each pulley to be 7.2 in, neglect friction, find internal forces at point J of the frame.

1st question that I have is whether the tension in section C-E of the cable also 90 lb? how about section C-D. Also, in my diagram of each of the members, I don't know how to label forces at point E where two long members and the pulley meet.

Finally, can someone gimme an idea how to go about doing this problem?
http://img487.imageshack.us/img487/8272/15am.jpg [Broken]
http://img487.imageshack.us/img487/4066/14ch.jpg [Broken]

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Last edited by a moderator: May 2, 2017
2. Oct 29, 2005

### Pyrrhus

Are points J and K joints? I think they are assuming pulleys have mass.

3. Oct 29, 2005

### physicsss

Last edited: Oct 29, 2005
4. Oct 29, 2005

### Pyrrhus

Yes, i'm familiar with internal forces [resultants of the stresses] (axial, shear and flexionant moment). First is to find the reactions and simply cut BE member at J, and solve for the shear force and flexionant moment.

5. Nov 1, 2005

### HeartbreakidX

I beleive you dont need to take pulleys into consideration you just find all the force around the member where point J is.
Then you just cut at point J and calculate everything again

6. Nov 1, 2005

### physicsss

I'm having trouble finding the vertical component of the force acting on frame B...any ideas? I set the moment about A zero and I was able to find the horizontal component of the force acting on frame B.

7. Nov 1, 2005

### Pyrrhus

Find the joint forces (E point) on the AE member then use them to find the vertical component of the reaction at B on the BE member.

8. Nov 1, 2005

### physicsss

I got 45 lb for the vertical component of the reaction force. is that right?

Last edited: Nov 1, 2005