Hanging masses

  • Thread starter physicos
  • Start date
  • #1
physicos
46
1

Homework Statement


A hanging mass M1 =1 kg is attached by a light string that runs over a frictionless pulley to a mass M2=2 kg that is initially at rest on a frictionles table .
What is the magnitude of the acceleration a of M2 ?


Homework Equations


I used for M1 :
Fg1 + T =M1a (with T tension of string)
and for M2 :
N+Fg2+T=M2a

The Attempt at a Solution


NOW I'm stuck , I can't solve it , any help ??
 

Answers and Replies

  • #2
Doc Al
Mentor
45,425
1,876
and for M2 :
N+Fg2+T=M2a
For M2 you have added forces that are perpendicular to each other. Don't do that! Instead, consider horizontal forces separately. (Assuming the table is horizontal, that's the direction of the acceleration.)

Be careful with signs.
 
  • #3
physicos
46
1
What I have written are vectors :
for M1 without vectors :
_m1g+T=-m1a
and for M2 :
N+T-m2g=m2a

I still didn't get your point
 
  • #4
Doc Al
Mentor
45,425
1,876
What I have written are vectors :
for M1 without vectors :
_m1g+T=-m1a
Good. (Note that the forces of gravity and tension all act vertically.)

and for M2 :
N+T-m2g=m2a
This combines vertical forces (N, mg) with horizontal forces (T). Don't do that.
 
  • #5
physicos
46
1
I thought T was a vertical force too
 
  • #6
Rellek
107
13
I thought T was a vertical force too

On mass 1 it is a vertical force. On m2 it is pulling from the side. Remember that since your pulley is massless and frictionless, the tension along the string will be completely constant.
 
  • #7
Doc Al
Mentor
45,425
1,876
I thought T was a vertical force too
Not when it acts on M2, which slides along a horizontal table. (A picture would help.)
 
  • #8
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
38,449
7,958
Not when it acts on M2, which slides along a horizontal table. (A picture would help.)
The OP doesn't actually state the orientation of the string between pulley and M2. Yes, it's probably meant to be horizontal, but in principle could be anything.
 
  • #9
physicos
46
1
so what am I supposed to do ? Cause that's all what is available in the problem statement , there is no picture : Should I work with it as a horizontal force ?
 
  • #10
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
38,449
7,958
so what am I supposed to do ? Cause that's all what is available in the problem statement , there is no picture : Should I work with it as a horizontal force ?
Yes.
 

Suggested for: Hanging masses

Replies
12
Views
632
Replies
10
Views
683
  • Last Post
2
Replies
49
Views
883
Replies
6
Views
678
Replies
23
Views
696
Replies
8
Views
448
Replies
16
Views
579
Replies
40
Views
652
  • Last Post
Replies
8
Views
258
Top