What is the magnitude of the force in this vector and forces problem?

[jsmith613]

Homework Statement

http://s359.photobucket.com/albums/oo40/jsmith613/?action=view&current=Vector-3.png
please help me with this question

thanks

could you also tell me how to find the magnitude of the force

thanks

The Attempt at a Solution

I presumed that gravity has a role in it but can't work out how the normal force is cancelled.

could someone please explain (maybe even with a diagram)

thanks

Homework Equations

None relevant

 

[berkeman]

Homework Statement

http://s359.photobucket.com/albums/oo40/jsmith613/?action=view&current=Vector-3.png
please help me with this question

thanks

could you also tell me how to find the magnitude of the force

thanks

The Attempt at a Solution

I presumed that gravity has a role in it but can't work out how the normal force is cancelled.

could someone please explain (maybe even with a diagram)

thanks

Homework Equations

None relevant

Start by drawing a free body diagram (FBD) of the mass on the ramp...

 

[jsmith613]

Start by drawing a free body diagram (FBD) of the mass on the ramp...

Oh, that was added with the question, here it is:

http://s359.photobucket.com/albums/oo40/jsmith613/?action=view&current=FreeBody.png

 

[berkeman]

Oh, that was added with the question, here it is:

http://s359.photobucket.com/albums/oo40/jsmith613/?action=view&current=FreeBody.png

Good start. Now add the two vectors in rectangular coordinates. Which way does the resulting acceleration have to point?

 

[jsmith613]

Good start. Now add the two vectors in rectangular coordinates. Which way does the resulting acceleration have to point?

I don't understand why I use rectangular coordinates. for 100 g mass I am only interested in gravity so accelaration should be down?

 

[berkeman]

I don't understand why I use rectangular coordinates. for 100 g mass I am only interested in gravity so accelaration should be down?

Vectors are easiest to add in rectangular coordinates. Because of the ramp, the resulting vector acceleration has to be parallel to the ramp.

 

[jsmith613]

Vectors are easiest to add in rectangular coordinates. Because of the ramp, the resulting vector acceleration has to be parallel to the ramp.

But if we add vectors in such a way, then surely we will get an overall force that is double

http://s359.photobucket.com/albums/oo40/jsmith613/?action=view&current=FreeBody-1.png

If we look at the extra boxes (rectangles) and we add the total force along the top and along the bottom we will get a force double what we want and it is unlikley to yield a straight line as we have curently