# Homework Help: Magnitude of Force within incline?

1. Sep 27, 2007

### anglum

Magnitude of Force within incline?????

A block with mass of 5.5kg is held in equilibrium on a frcitionless incline of 34 degrees by the horizontal force F. The acceleration of gravity is 9.81m/s^2

What is the magnitude of F? answer in units of N

What is the magnitude of the normal force? answer in units of N

I converted 5.5 kg to 53.9N

then i used sin of 56 degrees * 53.9 to get the horizontal force of 44.68N

then i used cos of 56 degrees * 53.9 to get the normal force of 30.14N

2. Sep 27, 2007

because you need to use sin of 34 not 56 degrees. you have the basic concept of weight the the triangle it forms. but that triangle is proportional the incline, so they have the same angles.

3. Sep 27, 2007

### anglum

ok but sin of 34 * 53.9 = 30.14N

and cos of 34 * 53.9 = 44.68N

so i get the same answers ..... and they are wrong... thats why i am stuck

4. Sep 27, 2007

### johnsonandrew

Yeah, use 34 degrees, not 56. Fh= Fg*(sin x)
Your angle of incline will be the angle you use in the computation.

so Fh= (54.0)*(sin 34) = 30.2 N
and Fn= (54.0)*(cos 34) = 44.8 N

Double check my work.. but I think thats how you do it..

5. Sep 27, 2007

### johnsonandrew

Is there additional information in the problem you didn't include? Because I believe that's correct...

6. Sep 27, 2007

### anglum

those answers are incorrect... thats why i am so lost

7. Sep 27, 2007

### anglum

the drawing shows the incline... the slope of the incline is 34 degrees... the block on it is 5.5 kg which is 53.9N

it slopes up from left to right... there is a line horizontal that is labeled as F.. and above it is a arrow pointing down sayin 34 degrees as well....

where this horizontal line F touches the block is in the top left corner of the block... then an angled line down off of the top left corner of the block slopes down the incline as well

8. Sep 27, 2007

those look correct to me too

9. Sep 27, 2007

### anglum

i wish there was a way to draw out what they give u .... i tried to describe it the best i could

10. Sep 27, 2007

### anglum

this is the best that i can describe the drawing shows the incline... the slope of the incline is 34 degrees... the block on it is 5.5 kg which is 53.9N

it slopes up from left to right... there is a line horizontal that is labeled as F.. and above it is a arrow pointing down sayin 34 degrees as well....

where this horizontal line F touches the block is in the top left corner of the block... then an angled line down off of the top left corner of the block slopes down the incline as well

its an online class so when i enter the answer it tells me its wrong

11. Sep 27, 2007

did you round before the answer? maybe you need to round only after finding the answer. that can change it by .1 or .01 or whatever

12. Sep 27, 2007

### johnsonandrew

and the horizontal comes from the left?

13. Sep 27, 2007

### anglum

i tried answers ranging from 30..05 to 30.2 and the same for 44.65 to 44.70

and they were wrong

14. Sep 27, 2007

### johnsonandrew

Yeah, since its an online course where you enter the answer that might throw it off. Try my answers, I was careful with significant figures...

15. Sep 27, 2007

### anglum

i am uploading the picture of the problem online.. i will have the link for u to see it in one minute

16. Sep 27, 2007

### johnsonandrew

But I believe since the horizontal force touches the top left corner, and not the center of the block, it does not equal F parallel, so the formula does not apply... Let me give it another shot on paper...

17. Sep 27, 2007

### anglum

18. Sep 27, 2007

### johnsonandrew

Awesome, that would help a lot.

19. Sep 27, 2007

### anglum

check that link for the drawing of the problem

20. Sep 27, 2007

### johnsonandrew

Ok, give me a minute I'll figure it out if someone doesn't before me.