Any questions?? Please ask/answer questions regarding this homework problem through the "Leave a Comment" link above.

## 17 thoughts on “Homework H.4.C”

### Leave a Reply

You must be logged in to post a comment.

Any questions?? Please ask/answer questions regarding this homework problem through the "Leave a Comment" link above.

You must be logged in to post a comment.

For all questions, do we consider g=9.8 or g=-9.8?

I think it depends on what they call the vertical axis and how you orient it. So if you have a regular Cartesian x and y axis, gravity would be -9.8 because it is in the negative direction, but if your coordinate system is upside down, then it would be a positive value.

How do we find the tensions in the ropes in terms of given quantities?

I wrote the x and y equations for both blocks, then found all of the tensions in terms of one tension (I used to the tensions between block A and the pulley C). Then you can substitute so you only have tension, force, and mass left. Then plug it into F=ma.

Would it be sensible to place the coordinate axes such that the x-axis is parallel to the incline?

Yeah, that's what I did. It requires a lot less trig that way!

What terms, at most, do we leave the answer in?

I think you only need m, g, and F.

If you orient the coordinate system so that the x is parallel with the inclined surface, then just m,g, and F. But if you leave the system parallel with the diagram, then you'd need theta as well.

Since they didn't specify in the instruction I left my final terms in F,m, and g.

I placed the coordinate system x parallel with the incline, and i still got theta in my answer. Are we supposed to have theta in the accelerations of block A and B?

Be confident if you considered the contribution of gravitational force in your Newton’s equation.

Yes, θ will appear in your final answers - the accelerations of the blocks do depend on the angle of the incline.

Is the effect of the pulleys that A is holding 1/4 of the weight of B and B is getting 1/4 the effect of F, or is it more complicated than that?

I believe it is more complicated than that. Since block A has a net acceleration, F is not necessarily equal to the tension on pulley A.

Is there a need for the length of each of the pullies because the cable is not one continuous piece?

Do we have to use s to solve this?