Calculating Bridge Pillar Forces: Solving a Seesaw Problem

It seems like you have a good understanding of the principles involved. Just to clarify, in this problem there is no torque because the forces are acting vertically and not creating any rotational motion. So in summary, the problem involves a 20 m long bridge with a weight of 400,000 N, supported by two pillars 3 m from each end. A 19,600 N car is parked 8 m from one end. The pillars exert equal and opposite forces to keep the bridge in static equilibrium, and can be calculated using equations for force and moments.
  • #1
jjjsarnis
15
0
the problem reads:

a uniform bridge 20 m long and weighing 400,000 N is supported by two pillars located 3 m from each end. if a 19,600 N car is parked 8 m from one end of the bridge, hoe much force does each pilliar exert?

i was thinking about using something like (W1)(d1) = (W2)(d2) that we used early for a seesaw problem. also if the sum of forces could be added up to equal zero and place it in equilibrium.

thanks for any help
 
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  • #2
Well you're sort of on the right track. First of all, the net force would be zero. This is because the system is in static equilibrium. I'm not sure which seesaw problem you're referring to but (W1)(d1) = (W2)(d2) would not help. If a system is in static equilibrium, there are two things that must be true. First of all, the net force is zero. What is the other one?
 
  • #3
Consider the forces acting on the bridge. You should have the weight of the car and two normal reaction forces (one each from each of the pillars). Make a simple equatio relating those three forces. Now consider moments about one of the pillars (it doesn't matter which, just pick one). Make another equation for the balance of the moments. Now you have two simple simultaneous equations in two variables (the two reaction forces). Solve for them and you have your answer.
 
  • #4
thanks guys, the other thing in static equilibrium would be net torque would equal zero but i didnt think there was any torque in this sytem, thanks again for your help
 
  • #5
Great job!
 

1. What is the force on a bridge?

The force on a bridge is the total amount of external or internal load that is acting on the structure of the bridge. This force can be caused by the weight of the bridge itself, the weight of the objects or vehicles on the bridge, environmental factors such as wind or water, and the force of gravity.

2. How is the force on a bridge calculated?

The force on a bridge is typically calculated using the principles of statics and structural analysis. This involves considering the different forces acting on the bridge, such as tension, compression, and shear, and using equations and diagrams to determine the magnitude and direction of these forces.

3. Why is it important to understand the force on a bridge?

Understanding the force on a bridge is crucial for ensuring the safety and stability of the structure. Bridges are designed to withstand specific amounts of force, and failure to accurately calculate and account for these forces can lead to structural damage or collapse.

4. How does the force on a bridge affect its design?

The force on a bridge directly impacts its design, as the structure must be able to withstand and distribute these forces without failing. The type of forces acting on the bridge will also influence the type of materials, shape, and construction methods used in the design process.

5. What factors can increase the force on a bridge?

The force on a bridge can be increased by various factors, such as heavy traffic or loads, extreme weather conditions, and structural damage or deterioration over time. Additionally, changes in the surrounding environment, such as erosion or ground movement, can also impact the force on a bridge.

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