Resolving forces in equilibrium on inclined plane

  • #1
5
1

Homework Statement


Solve for the forces P and N acting on an object in equilibrium on an inclined plane.
Weight=10N, angle is 30 degrees
http://blob:https%3A//www.physicsforums.com/d431a152-5681-411b-ba57-809320539165
upload_2015-11-22_10-13-35.png

Homework Equations


Trigonometry, i.e. sin, cos, tan rules. The 'Z' rule (amongst others) to determine angles.

The Attempt at a Solution


I have attempted the problem (as done with similar problems, which were correct) however the answers seem to assume that the angle in solving P is 30.
I have used in the Parallel P=10tan60=17.32N. However the answer is given by 10tan30=5.77N. Is the answer wrong? Or have I made inaccurate assumptions?
upload_2015-11-22_10-16-1.png

In the perpendicular, N=10sin60=8.66N, however this is wrong also! The answer is given by 10/sin60
upload_2015-11-22_10-25-36.png

Thankyou for any help.
 

Answers and Replies

  • #2
569
85
Assume a frictionless plane.

Resolve N into X and Y directions and it will become clear.
 
  • Like
Likes Issy04
  • #3
1,065
10
Assume a frictionless plane.

Resolve N into X and Y directions and it will become clear.
The Y component of N is used to support 10N object from moving down vertically. Since we resolve N into components, then there must also be an X component.
Once you resolved N into components, N does not exist anymore but 4 forces acting on the object.
 
Last edited:
  • Like
Likes Issy04
  • #4
5
1
The Y component of N is used to support 10N object from moving down vertically. Since we resolve N into components, then there must also be an X component.
Once you resolved N into components, N does not exist anymore but 4 forces acting on the object.
Thank you. I have calculated the correct value of P now but I am still confused as to why N does not equal 10sin60, as P has no vertical component?
 
  • #5
ehild
Homework Helper
15,525
1,901
The resultant of the 10 N force and P must be equal and opposite to N.

upload_2015-11-22_6-54-4.png
 

Attachments

  • Like
Likes Issy04
  • #6
1,065
10
Thank you. I have calculated the correct value of P now but I am still confused as to why N does not equal 10sin60, as P has no vertical component?
Now we try to solve using triangular method since net forces equal to zero.
As you you know you can place the vector, the arrow anywhere, parallel and pointing to same direction.
10N is the base, P is opposite, and N is hypothenus.
 
  • Like
Likes Issy04
  • #7
5
1
Now we try to solve using triangular method since net forces equal to zero.
As you you know you can place the vector, the arrow anywhere, parallel and pointing to same direction.
10N is the base, P is opposite, and N is hypothenus.
Thank you very much! It is clear now.
The resultant of the 10 N force and P must be equal and opposite to N.

View attachment 92220
 

Related Threads on Resolving forces in equilibrium on inclined plane

  • Last Post
Replies
2
Views
4K
  • Last Post
Replies
12
Views
9K
  • Last Post
Replies
2
Views
25K
  • Last Post
Replies
1
Views
588
Replies
3
Views
15K
  • Last Post
Replies
2
Views
1K
Replies
6
Views
10K
Replies
3
Views
3K
  • Last Post
Replies
6
Views
2K
  • Last Post
Replies
6
Views
4K
Top