Math Problem Statement

A uniform 5.09 m long horizontal beam that weighs 435 N is attached to a wall by a pin connection that allows the beam to rotate. Its far end is supported by a cable that makes an angle of 58° with the horizontal, and a 481 N person is standing 2.01 m from the pin. Find the force FT in the cable by assuming that the origin of our coordinate system is at the rod’s center of mass. Find the magnitude of the force R exerted on the beam by the wall if the beam is in equilibrium.

Solution

Part 1 (Problem 005):

We are tasked with finding the tension force FTF_T in the cable. Since the beam is in equilibrium, we will use the conditions of static equilibrium:

  1. Sum of forces in the horizontal and vertical directions must be zero.
  2. Sum of torques (moments) about any point must be zero.

Let's choose the pivot point at the wall where the beam is attached (pin connection). This will eliminate the reaction forces at the pin in the torque equation.

Torque Calculation:

We need to ensure the beam is in rotational equilibrium. Let the length of the beam be L=5.09mL = 5.09 \, \text{m}.

  • Weight of the beam = 435N435 \, \text{N}, acting at its center (at 2.545m2.545 \, \text{m} from the pin).
  • The 481 N person stands at a distance of 2.01m2.01 \, \text{m} from the pin.
  • The tension in the cable creates a torque about the pin. The cable is at an angle of 5858^\circ, and the moment arm of the tension is L=5.09mL = 5.09 \, \text{m}.

The torque equation around the pin: Sum of torques=0\text{Sum of torques} = 0 Clockwise torque due to the weight of the beam and the person: τweight of beam=435N×2.545m\tau_{\text{weight of beam}} = 435 \, \text{N} \times 2.545 \, \text{m} τweight of person=481N×2.01m\tau_{\text{weight of person}} = 481 \, \text{N} \times 2.01 \, \text{m} Counterclockwise torque due to the tension in the cable (only the vertical component contributes to torque): τT=FT×sin(58)×5.09m\tau_{T} = F_T \times \sin(58^\circ) \times 5.09 \, \text{m}

Setting the total torque equal to zero: FT×sin(58)×5.09=(435×2.545)+(481×2.01)F_T \times \sin(58^\circ) \times 5.09 = (435 \times 2.545) + (481 \times 2.01) Solving for FTF_T: FT=(435×2.545)+(481×2.01)sin(58)×5.09F_T = \frac{(435 \times 2.545) + (481 \times 2.01)}{\sin(58^\circ) \times 5.09}

Let me calculate this value.The tension force FTF_T in the cable is approximately 480.45N480.45 \, \text{N}.


Part 2 (Problem 006):

Now, we need to find the magnitude of the reaction force RR exerted on the beam by the wall. Since the beam is in equilibrium, the sum of forces in both the horizontal and vertical directions must also be zero.

  • Horizontal forces: The horizontal component of the tension FTF_T is balanced by the horizontal reaction force at the wall RxR_x.

    Rx=FTcos(58)R_x = F_T \cos(58^\circ)

  • Vertical forces: The vertical reaction force RyR_y at the wall balances the vertical component of the tension and the total weight (beam + person).

    Ry+FTsin(58)=435N+481NR_y + F_T \sin(58^\circ) = 435 \, \text{N} + 481 \, \text{N}

After solving for RxR_x and RyR_y, we can combine them to find the total reaction force RR using:

R=Rx2+Ry2R = \sqrt{R_x^2 + R_y^2}

Let me calculate this for you.The reaction force RR exerted on the beam by the wall is approximately 568.73N568.73 \, \text{N}.


Would you like any further details or explanations about these calculations? Here are a few related questions for deeper understanding:

  1. What happens if the angle of the cable changes? How does it affect the tension FTF_T?
  2. How would the problem change if the person stood closer to the pin?
  3. What if the beam was longer or shorter? How would it impact the forces?
  4. Can you explain why we neglect the horizontal forces in the torque calculation?
  5. What would happen if there was no pin at the wall? How would the system behave?

Tip: In static equilibrium problems, breaking down forces into their horizontal and vertical components can help simplify the problem-solving process.

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Math Problem Analysis

Mathematical Concepts

Statics
Equilibrium
Torque
Force Components

Formulas

Sum of torques = 0
Sum of horizontal forces = 0
Sum of vertical forces = 0
Torque = Force × Distance × sin(θ)
Resultant Force: R = √(Rx² + Ry²)

Theorems

Static Equilibrium Conditions

Suitable Grade Level

Grades 11-12, College Physics