• Support PF! Buy your school textbooks, materials and every day products Here!

Wedge problem

  • Thread starter gracy
  • Start date
  • #26
2,486
82
because the normal force changes.
Why normal force changes?
 
  • #27
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
32,363
4,893
Why normal force changes?
Because the accelerations of the wedge and block change, and because the angle changes.
A full analysis of the dynamics would be a bit of a challenge, and I suspect wll beyond what you are expected to do here. The question as posed is answered by the simple logic I've outlined. The wedge will be at max and min speeds when there is no horizontal force on it, and that will be when the block is at the lowest point. By momentum conservation, if the block is moving to the left relative to the wedge it will be the max, if to the right it will be the min.
 
  • #28
2,486
82
The wedge will be at max and min speeds when there is no horizontal force on it,
Because as long force is there ,acceleration will also be there and so velocity will go on increasing and there will not be any instant when we can say that it is maximum velocity that's why when there is no horizontal force no acceleration as well as deceleration ,at that moment velocity will be maximum and that is certainly the midpoint of depression.Right?One more thing
Velocity of wedge at mid point of depression is equal to velocity of wedge just before coming at mid point of depression when there was horizontal force acting on wedge.
 
Last edited:
  • #29
2,486
82
Please tell me my post #28 is correct or not?
 
  • #30
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
32,363
4,893
Velocity of wedge at mid point of depression is equal to velocity of wedge just before coming at mid point of depression when there was horizontal force acting on wedge.
I don't understand. If the block is not at the middle of the depression then the speed of the wedge is changing.
 
  • #31
2,486
82
Because as long force is there ,acceleration will also be there and so velocity will go on increasing and there will not be any instant when we can say that it is maximum velocity that's why when there is no horizontal force no acceleration as well as deceleration ,at that moment velocity will be maximum and that is certainly the midpoint of depression.Right?
Is this correct?
 
  • #32
2,486
82
If the block is not at the middle of the depression then the speed of the wedge is changing.
But it must be having some instantaneous velocity just before coming to mid point of depression.
 
Last edited:
  • #33
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
32,363
4,893
But it must be having some instantaneous velocity just before coming to mid point of depression.
Yes... so?
 
  • #34
2,486
82
But it must be having some instantaneous velocity just before coming to mid point of depression.
But it must be having some instantaneous velocity just before the block comes to mid point of depression.[/QUOTE]By it I mean wedge.
 
  • #35
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
32,363
4,893
But it must be having some instantaneous velocity just before the block comes to mid point of depression.
By it I mean wedge.[/QUOTE]
I agreed the wedge would have some instantaneous velocity before the block reaches the mid point. But it will not be quite as much as when the block is at the mid point.
 
  • #36
2,486
82
But it will not be quite as much as when the block is at the mid point.
Why?
 
  • #37
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
32,363
4,893
Why?
Because as long as the block is not exactly at the mid point the normal force will have a horizontal component, accelerating the wedge.
 
  • #38
2,486
82
Because as long as the block is not exactly at the mid point the normal force will have a horizontal component, accelerating the wedge.
That's why I have used the term just before coming at mid point.So that there will not be any horizontal force after that.
 
  • #39
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
32,363
4,893
It
That's why I have used the term just before coming at mid point.So that there will not be any horizontal force after that.
It's either at the mid point or it isn't. If it's not at the midpoint then there is a horizontal force, no matter how small.
 

Related Threads for: Wedge problem

  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
2
Views
6K
  • Last Post
Replies
6
Views
2K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
7
Views
2K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
18
Views
3K
Top