Finding minimum force to pull the napkin out from under the tea cup

  • Thread starter Jpyhsics
  • Start date
  • #1
84
2

Homework Statement


There is a table, and a napkin on it. The napkin has a mass mn=71.6 g. On the napkin, there is a tea cup with mass mc=104.6 g. What is the minimum force required for someone to pull the napkin out from under the tea cup? Assume that between the table and the napkin the friction is µk= 0.484, while the coefficient of static friction between the tea cup and the napkin is µs=0.705. Express your answer in Newtons.

Homework Equations


F=ma

The Attempt at a Solution


ΣFxNapkin=F-frC-frT (where C is cup and T is table)
ΣFxCup=frN (where N is napkin)

I have also included a photo of my FBD
How can I proceed with this question? Do I have a correct FBD?
 

Attachments

  • IMG_109F6D002955-1.jpeg
    IMG_109F6D002955-1.jpeg
    28.9 KB · Views: 323

Answers and Replies

  • #2
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
2020 Award
35,869
6,591
How can I proceed with this question? Do I have a correct FBD?
Your FBD looks fine.
What about the cup's acceleration?
 
  • #3
84
2
Your FBD looks fine.
What about the cup's acceleration?
Would the acceleration of the cup be equal to the acceleration of the napkin?
 
  • #4
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
2020 Award
35,869
6,591
Would the acceleration of the cup be equal to the acceleration of the napkin?
Yes, or only very slightly less. So what equation can you write?
 
  • #5
84
2
so would the cup acceleration be:
ackg ?
Which subsequently would be the acceleration of the napkin?

So would my solution in the picture make sense?
 

Attachments

  • IMG_E3E262A0D1DA-1.jpeg
    IMG_E3E262A0D1DA-1.jpeg
    37.8 KB · Views: 297
  • #6
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
2020 Award
35,869
6,591
so would the cup acceleration be:
ackg ?
μk is the kinetic friction between the napkin and the table.
 
  • #8
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
2020 Award
35,869
6,591
Okay thanks!
Not sure how to interpret that response. I am telling you that your equation in post #5 makes no sense... and wondering if it was a typo.

Edit: I have marked the thread unsolved.
 
Last edited:

Related Threads on Finding minimum force to pull the napkin out from under the tea cup

Replies
1
Views
3K
  • Last Post
Replies
5
Views
2K
Replies
11
Views
14K
Replies
5
Views
3K
  • Last Post
Replies
1
Views
6K
  • Last Post
Replies
11
Views
1K
Replies
1
Views
2K
Replies
12
Views
288
  • Last Post
Replies
1
Views
3K
Top