Is my vertical component calculation correct?

In summary, the conversation discusses two methods for determining the vertical component of the force exerted by the pin at D on the beam A-D, which return different answers. The first method involves taking moments about A and solving for D_y, while the second method involves taking moments about B and using the equation $\sum M_B = -40(1.5)-50(2)-(50-T)(2)+4(V)=0$. However, there seems to be an error in both methods, with the first method using the incorrect force of $(T-50)$ instead of $(50-T)$ and the second method missing a $T$ term and including an unexplained $-50(2)$ term.
  • #1
Dethrone
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In the structure shown, a cable is attached to the 50 kN weight and to the beam A-D at point B. If the horizontal uniform beam weighs 8 kN/m, determine the following:
(a) The horizontal and vertical component of the force that the pin at D exerts on the beam A-D.
(b) The force in the cable.
...

View attachment 3383

I just want to focus on getting the vertical component right...and I have developed two methods, each of which return a different answer.
1) Taking moments about A (i know doing it about B is simpler):
$$\sum M= T_y -40(2.5)-(T-50)(3)+D_y(5)$$
$$\sum F_y = T_y-40-50+D_y =0$$
$$=T \sin36.9-90+D_y$$

Now solving the two equations, I get $D_y = 61.98 \text{kN}$2) Starting with this line...
$$\sum M_B = -40(1.5)-50(2)-(50-T)(2)+4(V)=0$$

Any of them correct?
 

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  • #2
Rido12 said:
In the structure shown, a cable is attached to the 50 kN weight and to the beam A-D at point B. If the horizontal uniform beam weighs 8 kN/m, determine the following:
(a) The horizontal and vertical component of the force that the pin at D exerts on the beam A-D.
(b) The force in the cable.
...

https://www.physicsforums.com/attachments/3383

I just want to focus on getting the vertical component right...and I have developed two methods, each of which return a different answer.
1) Taking moments about A (i know doing it about B is simpler):
$$\sum M= T_y -40(2.5)-(T-50)(3)+D_y(5)$$
$$\sum F_y = T_y-40-50+D_y =0$$
$$=T \sin36.9-90+D_y$$

Now solving the two equations, I get $D_y = 61.98 \text{kN}$2) Starting with this line...
$$\sum M_B = -40(1.5)-50(2)-(50-T)(2)+4(V)=0$$

Any of them correct?

Doesn't look like it. (Doh)

In the first method, you have a force of $(T-50)$ that would act in a clockwise fashion (negative).
However, $T$ is upward while $50\text{ kN}$ is downward.
So the force should be $(50-T)$ instead.

Furthermore, in the sum of the vertical forces I seem to be missing a $T$ term. :eek:

In the second method I'm assuming that with $V$ you mean the same thing as $D_y$.
Anyway, here you do have the direction of the $(50-T)$ correct!
But... where is the $-50(2)$ term coming from? (Wondering)
 

FAQ: Is my vertical component calculation correct?

What is a moment in physics?

A moment in physics refers to the turning effect produced by a force acting on an object. It is calculated by multiplying the magnitude of the force by the perpendicular distance from the point of rotation to the line of action of the force. Moments are important in understanding the equilibrium and stability of objects.

How is tension defined in science?

In science, tension is defined as the pulling force exerted by an object or material when it is stretched or pulled. It is a type of mechanical stress and can be measured in units of force, such as Newtons. Tension is an important concept in studying the strength and elasticity of materials.

What causes stress in materials?

Stress in materials is caused by the application of external forces, such as tension, compression, or shear. These forces can cause changes in the shape or size of the material, leading to internal strains within the material. Stress can also be caused by thermal expansion or contraction, chemical reactions, or changes in pressure.

How does stress affect the behavior of materials?

Stress can affect the behavior of materials in several ways. It can cause the material to deform or break, depending on its strength and elasticity. Stress can also cause changes in the physical and chemical properties of the material, such as changes in conductivity or magnetism. Additionally, stress can affect the overall stability and durability of a material.

How do scientists measure stress in materials?

Scientists use a variety of methods to measure stress in materials, depending on the type of stress and the properties of the material. Some common techniques include strain gauges, which measure changes in length or shape of a material, and optical methods, which use light to detect changes in surface shape or stress. Other methods include ultrasonic testing, X-ray diffraction, and mechanical testing.

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