Finding the critical angle.

  • #1
7
0

Homework Statement


A force F is applied to a box of mass M at an angle θ below the horizontal (see figure). The coefficient of static friction between the box and the floor is μs, and the coefficient of kinetic friction between the two surfaces is μk.

a) What is the minimum value of F to get the box to start moving from rest?
b) What is the minimum value of F so that the box will move with constant velocity? (Assuming it's already moving.)
c) If θ is greater than some critical angle θcrit, it is impossible to have the scenario described in part b. What is θcrit ?

Homework Equations


I figured out part a which is μs*mg/cosθ-μssinθ. Then part b which is the same equation except with μk instead of μs.

The Attempt at a Solution


Honestly, I don't even know where to start. My professor has never gone over problems with critical angles. Is there a formula I can use to solve this?
 

Answers and Replies

  • #2
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
2020 Award
37,204
7,297
Honestly, I don't even know where to start
Look at your answer to part b. Part c is saying that if theta is too large then no F is large enough. At what value of theta does F get impossibly large?
 
  • #3
BvU
Science Advisor
Homework Helper
14,612
3,822
Hi Watney, :welcome:
You start with a drawing (probably you did that already).
The formula you are looking for is called Newton's law. Constant velocity requires a zero sum of forces.

[edit] Ha! Haru was quicker and brought you even closer to your solution. Lucky you !
 

Related Threads on Finding the critical angle.

  • Last Post
Replies
2
Views
3K
R
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
3
Views
1K
Replies
3
Views
3K
  • Last Post
Replies
3
Views
10K
  • Last Post
Replies
1
Views
937
  • Last Post
Replies
1
Views
6K
  • Last Post
Replies
7
Views
9K
  • Last Post
Replies
6
Views
4K
Top