Solving Gravitational Torque Homework Equations

[mintsnapple]

Homework Statement

Homework Equations

torque = r*Fsin(x)

The Attempt at a Solution

I really need help on walking through this problem...didn't really teach it in class...I tried watching a video and you're supposed to sum the forces * some perpendicular distance to the pivot? Yet what if the force is already perpendicular?

 

[CWatters]

Check your force diagram for missing and incorrect forces acting on the beam.

T2 is the tension force acting on the mass m (eg not acting on the end of the beam).

Your equation has force T1 acting at what distance from the pivot? Let's say the beam has length L so d = Lcos(60). Then T1 acts at h where h= Lsin(60) from the pivot.

The net torque on the beam should sum to zero because it's not rotating.

The net forces in x and y on the beam should also sum to zero because it's not translating.

 

[mintsnapple]

Check your force diagram for missing and incorrect forces acting on the beam.

T2 is the tension force acting on the mass m (eg not acting on the end of the beam).

Your equation has force T1 acting at what distance from the pivot? Let's say the beam has length L so d = Lcos(60). Then T1 acts at h where h= Lsin(60) from the pivot.

The net torque on the beam should sum to zero because it's not rotating.

The net forces in x and y on the beam should also sum to zero because it's not translating.

How does this look?

Also, how should I approach c? Is it just the weight of the beam?

 

[Tanya Sharma]

What are the forces acting on the weight of mass M ?

 

[CWatters]

There is a force on the beam at the pivot.

 

[mintsnapple]

There is a force on the beam at the pivot.

Could you please explicate?

 

[mintsnapple]

What are the forces acting on the weight of mass M ?

Gravity and the tension of cable 2.

 

[Tanya Sharma]

Gravity and the tension of cable 2.

Good...So considering that the weight is in equilibrium ,what is the relation between them ? You may refer tension as T₂ and weight Mg .

 

[mintsnapple]

Good...So considering that the weight is in equilibrium ,what is the relation between them ? You may refer tension as T₂ and weight Mg .

There is also a vertical force from the weight of the beam no? Which is M/2*G*sin60.

Also, how would I find the forces on the beam by the pivot?

 

[Tanya Sharma]

There is also a vertical force from the weight of the beam no? Which is M/2*G*sin60.

No..that is not correct.The weight of the beam is acting on the beam ,not on the weight .There are only two forces acting on the weight ;T₂ and Mg

So,what is the relation between them ?

Also, how would I find the forces on the beam by the pivot?

Let us call the force exerted by pivot as P .The horizontal component as P_x and vertical component as P_y .

Can you write the torque equation for the beam with respect to the pivot ?

Note :Please type your work.Do not paste an image.

 

[mintsnapple]

No..that is not correct.The weight of the beam is acting on the beam ,not on the weight .There are only two forces acting on the weight ;T₂ and Mg

So,what is the relation between them ?



Let us call the force exerted by pivot as P .The horizontal component as P_x and vertical component as P_y .

Can you write the torque equation for the beam with respect to the pivot ?

Note :Please type your work.Do not paste an image.

They are equal.

torque = px*sin60 + py*cos60 = 0?

 

[Tanya Sharma]

They are equal.

Yes. So T₂=Mg

torque = px*sin60 + py*cos60 = 0?

Simply wrong .

The pivot force does not feature in the torque equation of the beam about the pivot . It would have played a role if we were writing torque equation about the center of mass .

List all the forces acting on the beam .

 

[mintsnapple]

Yes. So T₂=Mg



Simply wrong .

The pivot force does not feature in the torque equation of the beam about the pivot . It would have played a role if we were writing torque equation about the center of mass .

List all the forces acting on the beam .

Just gravity?

 

[Tanya Sharma]

Just gravity?

It is only one of the forces acting on the beam .What about T₁ and T₂ ? Do you think any of them is acting on the beam ?

 

[mintsnapple]

It is only one of the forces acting on the beam .What about T₁ and T₂ ? Do you think any of them is acting on the beam ?

I apologize for my lack of knowledge and thank you so much for helping me.

I suppose T2 does pull the beam in the vertical direction and T1 pulls it in horizontal direction?

 

[Tanya Sharma]

Yes...

So,basically there are four forces acting on the beam ; T₁,T₂,Mg/2 and P .

Do you agree ?