• Support PF! Buy your school textbooks, materials and every day products Here!

Moving body on a diagonal path

  • Thread starter JAZZ541
  • Start date
  • #1
18
0

Homework Statement


Log A weighs 20Kg is laid on a diagonal smooth plane with a diagonal angle of 27 37 degree, log A is tied by a rope to the head of the plane and there through a wheel with no friction the rope descend vertically to the bottom of the plane and through another friction-less wheel is tied to log B that weighs 20 Kg and is laid on a smooth horizontal plane' the last part of the rope tied to log B is horizontal

Homework Equations


1. what is the time in which log A will move a 1 meter distance on the plane if it starts from rest?
2. what is the tension in the rope attached to both logs?

The Attempt at a Solution


is acceleration here 0? or maybe 6? I'm a bit lost would appreciate any help, thx!

physics1.jpg


[edit: fixed typo in given angle (picked up correction from post #3 -- Moderator]
 
Last edited by a moderator:

Answers and Replies

  • #2
Doc Al
Mentor
44,945
1,206
is acceleration here 0? or maybe 6?
Well, you know the acceleration can't be zero, else the first question would not make sense.

Do this: Analyze the forces acting on A and on B. Apply Newton's 2nd law to each.
 
  • #3
18
0
Ty!
Is this correct? btw angle is 37 and not 27
physics2.jpg
 
  • #4
Doc Al
Mentor
44,945
1,206
Well, you don't show arrows. (Forces have direction.) And what does "f" represent? How do t1 and t2 relate?
 
  • #5
18
0
f - friction ohh, but they said smooth surface, so no friction
and T1 = T2?
 
  • #6
Doc Al
Mentor
44,945
1,206
f - friction ohh, but they said smooth surface, so no friction
Right.

and T1 = T2?
Right. The tension is the same throughout the rope.
 
  • #7
18
0
I'm sorry I had to go ill try and work on it some more and come back later
 
  • #8
Doc Al
Mentor
44,945
1,206
I'm sorry I had to go ill try and work on it some more and come back later
No worries. Give it a shot and then come back and show what you've done.
 
  • #9
18
0
Thank u for your patience!
I have this:

1.

m1(A)g = m2(B)g = 20Kg

X = 1m

mag • sinα – T = m1a

T = m2a

mag • sinα -T + T = m1a + m2b

200 • 0.60 = a(m1 + m2)

a = 120/40 = 3m/s

X = V0T + at^2 /2

1 = 0 + 3t^2/2

2 = 3t^2

t = 0.816s

2.

T = m2a

T = 20 • 3 = 60N

there are two more questions about this problem:

3.
If there is a friction between log B and the horizontal surface what is the minimal static coefficient of friction in which if the system is in a state of rest then it will remain in that state?

4.
If the kinetic and static coefficient of friction is mu = 0.25, how long will it take log A to travel a 2 meter distance on the plane (the rope is weightless)?

how should I approach that?

Thx again!
 
  • #10
Doc Al
Mentor
44,945
1,206
m1(A)g = m2(B)g = 20Kg

X = 1m

mag • sinα – T = m1a

T = m2a

mag • sinα -T + T = m1a + m2b

200 • 0.60 = a(m1 + m2)

a = 120/40 = 3m/s
Good!
(1) Your first equation should be: ##m_1 = m_2 = 20## Kg
(2) Careful with units. Acceleration has units of m/s^2.
(3) It's almost always better to stick to symbols as long as possible before plugging in numbers. Here's how I'd do it:
Since the masses are the same, I'd use "m" for both masses. And since the acceleration is the same, I'd use "a" for that.
##mg\sin\theta - T = ma##
##T = ma##
Adding them, we get:
##mg\sin\theta = 2ma##
And so on.

Note that the mass cancels out! So it doesn't matter (at least for this part of the question).
X = V0T + at^2 /2

1 = 0 + 3t^2/2

2 = 3t^2

t = 0.816s
Good!

2.

T = m2a

T = 20 • 3 = 60N
Good!
 
  • #11
Doc Al
Mentor
44,945
1,206
3.
If there is a friction between log B and the horizontal surface what is the minimal static coefficient of friction in which if the system is in a state of rest then it will remain in that state?
(1) What additional force acts on B? (Use symbols, not numbers.)
(2) What is the acceleration?

Redo your force equations with this in mind.

4.
If the kinetic and static coefficient of friction is mu = 0.25, how long will it take log A to travel a 2 meter distance on the plane (the rope is weightless)?
This is similar to the first part, only now there is an additional force acting on B.
 
  • #12
18
0
TY!

(1) What additional force acts on B? (Use symbols, not numbers.)
(2) What is the acceleration?
a = 0 ?

Redo your force equations with this in mind.
mgsinα = T = f = mumg ?
 
Last edited by a moderator:
  • #13
Doc Al
Mentor
44,945
1,206
Good!

(I fixed your quotes.)
 
  • Like
Likes JAZZ541
  • #14
18
0
Then:
mu = sin37° = 0.6
Ty very very much for your patience and guidance!
 
  • #15
Doc Al
Mentor
44,945
1,206

Related Threads on Moving body on a diagonal path

  • Last Post
Replies
3
Views
753
Replies
5
Views
792
Replies
9
Views
767
Replies
8
Views
8K
Replies
2
Views
1K
Replies
5
Views
894
Replies
3
Views
2K
Replies
7
Views
385
Top