A block spins around a circle with thrust

  • Thread starter oneamp
  • Start date
  • #1
oneamp
219
0

Homework Statement


A 400g steel block rotates on a steel table while attached to a 1.20m -long hollow tube. Compressed air fed through the tube and ejected from a nozzle on the back of the block exerts a thrust force of 4.71N perpendicular to the tube. The maximum tension the tube can withstand without breaking is 60.0N . Assume the coefficient of kinetic friction between steel block and steel table is 0.60. (Figure 1)

If the block starts from rest, how many revolutions does it make before the tube breaks?


Homework Equations





The Attempt at a Solution



Fbreak = 60 N = mv^2/r → v = sqrt(60r/m) m/s = 180 m/s
a = F/m m/s^2 = 11.775 m/s^2
t = v/a = 15.2866242
s = at^2/2 = 1372.875167
theta = s/r = 1372.875167
revs = theta/(2pi) = 218.499...

Where am I going wrong? I only get a couple of more attempts then the question is locked out..... please help.

Thanks
 

Answers and Replies

  • #2
TSny
Homework Helper
Gold Member
13,653
3,837
Hello, oneamp.

In the first line of your solution, did you forget to take the square root?
 
  • #3
TSny
Homework Helper
Gold Member
13,653
3,837
Also, did you take into account the friction?
 
  • #4
oneamp
219
0
Yes those are both mistakes I made, thank you. Now I am trying to figure out where to put friction...
 
  • #5
TSny
Homework Helper
Gold Member
13,653
3,837
Now I am trying to figure out where to put friction...

Think about the direction of the friction force.
 
  • #6
oneamp
219
0
Ok I got it! Thank you very much for pointing those things out to me!
 

Suggested for: A block spins around a circle with thrust

  • Last Post
Replies
12
Views
770
Replies
13
Views
3K
  • Last Post
Replies
4
Views
6K
Replies
6
Views
703
  • Last Post
Replies
5
Views
2K
Replies
5
Views
10K
Replies
7
Views
2K
Replies
16
Views
461
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
1
Views
4K
Top