Help: Newton's Laws - cement bag at rest.

In summary, to find the tensions in the three wires holding a 339 N bag of cement in equilibrium, a free-body diagram is used to resolve the forces into their x and y components. Two equations are then made using the net force in the x and y directions. By substituting the value of T2 into the second equation, T1 can be solved for. The final equation is T1(sin62 + 0.961sin25) = 339.
  • #1
Illmatic
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Q: A bag of cement of weight 339 N hangs from three wires as suggested in the figure below. Two of the wires make angles and with the horizontal. If the system is in equilibrium, find the tensions in the wires?

pse6e.05.18p.e.jpg


The answer requires T1, T2, T3.

I know T3 = Fgravity = 339N.

I made a free-body diagram at the knot:

http://www.njsr.org/pics/albums/userpics/fbd.GIF

Now, I can resolve the forces into their x, y components:

T1: x: -T1(cos62) y: T1(sin62)
T2: x: T2(cos25) y: T2(sin25)
T3: x: 0 y: -339N

I can make the two required equations:

(1) Fnetx = T2(cos25) - T1(cos62) = 0

(2) Fnety = T1(sin62) + T2(sin25) - 339 = 0

I can solve (1) for T2 in terms of T1:

T2 = T1(cos62/cos25)
T2 = 0.961 T1

My problem occurs here, substituting T2 into (2) to get T1:

T1(sin62) + (0.961 T1)(sin25) - 339 = 0

I do not know how to solve for T1. Could someone be of assistance, and also double check that I got everything up until the point I was stuck, correct?

Thank you!

PS. This is first-year University Physics.
 
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  • #2
Now, I haven't bothered to check your numerical values; your approach has no flaws as far as I can see.
"T1(sin62) + (0.961 T1)(sin25) - 339 = 0"
Rewrite this as:

T1(sin62 + 0.961sin25) = 339
You should be able to solve it now.
 
  • #3
That helps tremendously. Thank you very much!
 

FAQ: Help: Newton's Laws - cement bag at rest.

What are Newton's Laws of Motion?

The three laws of motion, developed by Sir Isaac Newton, are fundamental principles that explain how objects move in the presence of forces. The laws are: 1) objects at rest stay at rest and objects in motion stay in motion with the same velocity unless acted upon by an unbalanced force, 2) the force applied to an object is equal to its mass multiplied by its acceleration, and 3) for every action, there is an equal and opposite reaction.

How do Newton's Laws apply to a cement bag at rest?

In the case of a cement bag at rest, the first law of motion applies. Since the bag is not moving, it will remain at rest unless acted upon by an external force. This means that the weight of the bag and the force of gravity acting on it are balanced, resulting in no movement.

What is the relationship between force, mass, and acceleration according to Newton's Second Law?

According to the Second Law of Motion, the force applied to an object is equal to its mass multiplied by its acceleration. This means that the greater the mass of an object, the more force is needed to accelerate it. Similarly, the greater the acceleration, the more force is needed to achieve it.

How does Newton's Third Law apply to the cement bag at rest?

The Third Law of Motion states that for every action, there is an equal and opposite reaction. In the case of the cement bag at rest, the force of gravity pulling the bag downwards is countered by an equal and opposite force exerted by the ground. This results in the bag remaining at rest.

Can Newton's Laws be applied to other objects besides the cement bag?

Yes, Newton's Laws of Motion can be applied to any object in motion, whether it is at rest or moving. These laws are universal and can be used to explain the behavior of all objects in the presence of forces.

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