# Atwood Machine Problem

1. Jun 30, 2014

### antonisz

1. A 77.00 Nt object (denoted as object 1) rests on the ground. A light cord is connected to this object which runs vertically upward over a light frictionless pulley and is attached to another object denoted as object 2.

a) Calculate the force that the ground exerts on object 1 if object 2 is 30 N.

b) Calculate the force that the ground exerts on object 1 if object 2 is 60 N.

c) Calculate the force that the ground exerts on object 1 if object 2 is 90 N.

http://imgur.com/cVEQW07 http://imgur.com/cVEQW07

g (m1 - m2) / (m1) + m2 = ay

I drew FBD's for both of the weights and solved for the acceleration for situation a. I then used the equation w - t = ma and solved for the tension value, I then subtracted the tension value from the original weight of object 1, and I got 33.88 N.

I feel like this is the wrong way of solving the problem because once you get to situation c, you would have a negative force which can't be possible.

2. Jun 30, 2014

### SammyS

Staff Emeritus
That seems to be a correct result for part c. -- but ...

If the ground can't produce a negative (downward) force on m1, then what do you suppose happens to the system?

#### Attached Files:

• ###### cVEQW07.png
File size:
5.6 KB
Views:
155
3. Jun 30, 2014

### antonisz

The system would change where object 1 would be "in the air" correct?

4. Jun 30, 2014

### SammyS

Staff Emeritus
Yes, so the ground will exert what force on m1?

5. Jun 30, 2014

### antonisz

It would have to be 0 Newton's. If I'm correct about that, then I already assumed that, however I rethought my approach on part a and b.

I redid the FBD's for (a) and (b) and added the two equations for Newton's second law, and the tensions canceled each other out, leaving me with w1 - w2 = Fn. From there I calculated that in situation (a), the force that the ground exerts is 47 Newton's, and in situation (b) it would be 17 Newton's.

Last edited: Jun 30, 2014
6. Jun 30, 2014

### SammyS

Staff Emeritus
That all looks good!

7. Jun 30, 2014

### antonisz

Thank you so much for the help!