Statics

[HATLEY1997]

Am I expressing the forces (n as normal reaction, f as friction force, t as in tension in rope, w as in weight) of the sandbag in the correct component format with the information given?

F=Niu
N=Nj
T=-Ti
W=-mgcos(60)j-mgsin(60)j

With m being the mass of the sandbag and T being 25g.

I do not know the coefficient of the static friction.

 

[blamocur]

If 'i' and 'j' are horizontal and vertical unit vectors respectively then your expressions are wrong. You might find it easier if you draw a diagram of all forces.

 

[HATLEY1997]

If 'i' and 'j' are horizontal and vertical unit vectors respectively then your expressions are wrong. You might find it easier if you draw a diagram of all forces.

 

[HATLEY1997]

I have drawn a diagram and attached this for some guidance - thank you!!

 

[The Highlander]

I do not know the coefficient of the static friction.

You don't need to know the coefficient of static friction.
The system is in equilibrium so all the forces must balance!

I have drawn a diagram and attached this for some guidance - thank you!!           

I don't know what your "N" is supposed to be but here is how I would start to draw the FBD; see if you can copy and complete that and then attempt to complete the problem as instructed...

​

NB: You may need to enlarge it somewhat to allow space for further annotations the question requires of you.

Hope that helps.

 

[HATLEY1997]

You don't need to know the coefficient of static friction.
The system is in equilibrium so all the forces must balance!


I don't know what your "N" is supposed to be but here is how I would start to draw the FBD; see if you can copy and complete that and then attempt to complete the problem as instructed...

View attachment 37594​

NB: You may need to enlarge it somewhat to allow space for further annotations the question requires of you.

Hope that helps.

That makes sense thank you. I will have a look at this.

I had N as normal reaction, F as friction force, T as in tension in rope, W as in weight - is this correct?

 

[blamocur]

If 'i' and 'j' are horizontal and vertical unit vectors respectively then your expressions are wrong. You might find it easier if you draw a diagram of all forces.

I realized that I somehow missed the definition of 'i' and 'j' in the statement of the problem -- sorry for the confusion.

 

[HATLEY1997]

I realized that I somehow missed the definition of 'i' and 'j' in the statement of the problem -- sorry for the confusion.is what I had correct?

That’s okay - so is what I had correct?

 

[blamocur]

W=-mgcos(60)j-mgsin(60)j

Don't you need both 'i' and 'j' in there?

If I were your teacher I would complain about 'mgcos' and 'mgsin' : do you mean 'M*g*cos...' ? Or, at least, 'M g cos...'
I'd also complain about things like "N=Nj" : one 'N' is a vector, another is a scalar, so you need to use different symbols there. I don't what kind of notations is expected in your class, but using the same symbol for different things is confusing.

 

[HATLEY1997]

Don't you need both 'i' and 'j' in there?

If I were your teacher I would complain about 'mgcos' and 'mgsin' : do you mean 'M*g*cos...' ? Or, at least, 'M g cos...'
I'd also complain about things like "N=Nj" : one 'N' is a vector, another is a scalar, so you need to use different symbols there. I don't what kind of notations is expected in your class, but using the same symbol for different things is confusing.

This not is the working out I have written down - i just wanted sure how to put the symbols in, however I should have used the * signs - my bad.

 

[khansaheb]

This not is the working out I have written down - i just wanted sure how to put the symbols in, however I should have used the * signs - my bad.

I would re-orient my i & j axis. x (i) axis will be along the slope (30º ConterClockWise from the horizontal direction). y (j) axis will be oriented 90º from x (i) axis.

Follow the conventional orientation i and j - life will be easier.

Stealing the diagram from response 5 - I would draw-

 

[The Highlander]

I would re-orient my i & j axis. x (i) axis will be along the slope (30º ConterClockWise from the horizontal direction). y (j) axis will be oriented 90º from x (i) axis.

Follow the conventional orientation i and j - life will be easier.

Stealing the diagram from response 5 - I would draw-
View attachment 37595

You (and anyone else) are, of course, welcome to "steal" any of my drawings, however, in my haste, I made some basic errors in constructing that drawing.
Here is a corrected (& more complete) version...

​

Hope that helps.