Two blocks held by a rope on an incline

  • Thread starter trolling
  • Start date
  • #1
trolling
14
0

Homework Statement



A block with mass m1 = 9.4 kg is on an incline with an angle θ = 31.0° with respect to the horizontal.

Now a new block is attached to the first block. The new block is made of a different material and has a coefficient of static friction μ = 0.9. What minimum mass is needed to keep the system from accelerating?

Homework Equations



Ft,1 = Ft,2
Fg,1 = m1*g
Fg,2 = m2*g
Fn,1= Fg,1*cos 31
Fn,2 = Fg,2*cos 31
Ff,s,2 = Fn*.9


The Attempt at a Solution



Ft,1 = Ft,2
Fg,1 = m1*g = 92.12N
Fg,2 = m2*g = m2*9.8
Fn,1= Fg,1*cos 31
Fn,2 = Fg,2*cos 31
Ff,s,2 = Fn*.9

I'm not really sure what to do after this. I have some free-body diagrams set up, but since I can't post them here, I can't show them.

I had a value for the coefficient of static friction, but that was for a system with a spring (.292), so I don't think that'll work here. I also have one for kinetic friction (.212), but that might not apply here. After that, I'm stuck.
 

Answers and Replies

  • #2
PhanthomJay
Science Advisor
Homework Helper
Gold Member
7,179
513
Please clarify this question, you are missing information.
 
  • #3
CWatters
Science Advisor
Homework Helper
Gold Member
10,545
2,317
Is the first block frictionless?
 
  • #4
trolling
14
0

Homework Statement



A block with mass m1 = 9.4 kg is on an incline with an angle θ = 31.0° with respect to the horizontal.

Now a new block is attached to the first block. The new block is made of a different material and has a coefficient of static friction μ = 0.9. What minimum mass is needed to keep the system from accelerating?

Homework Equations



Ft,1 = Ft,2
Fg,1 = m1*g
Fg,2 = m2*g
Fn,1= Fg,1*cos 31
Fn,2 = Fg,2*cos 31
Ff,s,2 = Fn*.9


The Attempt at a Solution



Ft,1 = Ft,2
Fg,1 = m1*g = 92.12N
Fg,2 = m2*g = m2*9.8
Fn,1= Fg,1*cos 31
Fn,2 = Fg,2*cos 31
Ff,s,2 = Fn*.9

I'm not really sure what to do after this. I have some free-body diagrams set up, but since I can't post them here, I can't show them.

I had a value for the coefficient of static friction, but that was for a system with a spring (.292), so I don't think that'll work here. I also have one for kinetic friction (.212), but that might not apply here. After that, I'm stuck.

The coefficients of friction are for the first block.
 
  • #5
PhanthomJay
Science Advisor
Homework Helper
Gold Member
7,179
513
Where's the rope? Please state the problem as written and provide a sketch if possible.
 
  • #6
CWatters
Science Advisor
Homework Helper
Gold Member
10,545
2,317
I'm sure this is a straightforward question but the way you have explained it is confusing...

For example..

Now a new block is attached to the first block. The new block is made of a different material and has a coefficient of static friction μ = 0.9. What minimum mass is needed to keep the system from accelerating?

is inconsistent with...

The coefficients of friction are for the first block.
 
  • #7
CWatters
Science Advisor
Homework Helper
Gold Member
10,545
2,317
If we take your original post at face value...

The first block is frictionless so it's simple to calculate the force down the slope due to gravity.

The second block has friction so you can write two equations, 1) for the force down the slope due to gravity and 2) for the friction force acting up the slope.

If the combination is static then the sum of all three forces equate to zero. Solve for the mass of the second block.
 

Suggested for: Two blocks held by a rope on an incline

  • Last Post
Replies
7
Views
399
Replies
44
Views
1K
Replies
1
Views
353
  • Last Post
Replies
19
Views
2K
Replies
11
Views
413
Replies
4
Views
806
Replies
6
Views
524
  • Last Post
Replies
6
Views
374
Replies
10
Views
529
Top