# How Is Torque Calculated in a Wrecking Ball Scenario?

In summary, the problem involves finding the torque exerted by a wrecking ball on a crane at point P, which is shown in a picture. The force applied by the wrecking ball is at an angle of 30 degrees with the horizontal, while the crane's 9m long boom is at an angle of 55 degrees with the horizontal. To calculate the torque, the perpendicular component of the force should be used, which is equal to 9800(sin85)(9).

## Homework Statement

At one point during its swing, a wrecking ball exerts a tension force of 9800 N on its cable, which makes an angle of 30 degrees with the horizontal. The crane's 9 m long boom is at an angle of 55 degrees with the horizontal. What is the torque exerted by the wrecking ball on the crane about an axis perpendicular to the page and passing through the point P shown in picture

here is a pic of the problem:
http://imgur.com/a/c4B0X

## Homework Equations

Torque = r * applied force

## The Attempt at a Solution

Well.. I have some questions first with this one.

Am I finding the torque at the point the cable meets the crane, or at point P? I guess I really don't know much about cranes at all I am not sure how they work so this adds to the confusion..

Also how am I suppose to find the length of the cable??

Am I finding the torque at the point the cable meets the crane, or at point P?
The problem statement says point P.
Also how am I suppose to find the length of the cable??
I don't think it's necessary if you are just finding the torque from the wrecking ball around point P.

TomHart said:
The problem statement says point P.

I don't think it's necessary if you are just finding the torque from the wrecking ball around point P.

So do I just multiply r (9 meters) * the force 9800 N?

the components doesn't matter right?

You have to take into account the angle of the force relative to the boom.

TomHart said:
You have to take into account the angle of the force relative to the boom.
I see that the angle of the force is 5 degrees off from the ideal 90 degrees. But how do I know which component to use now? The x component makes sense to me but I'm not sure..

I'm not sure how you are defining your x direction. But you should use the component of the 9800 N force that is perpendicular to the boom.

Edit: Look at force F2 in figure P12.45. Let's assume that force F2 is at an angle 30 degrees below horizontal. The component of the force that is perpendicular to that rod would be (F2)sin30.

TomHart said:
I'm not sure how you are defining your x direction. But you should use the component of the 9800 N force that is perpendicular to the boom.

Is 9800sin(30) * 9 m the same answer you got?

30 degrees is the angle that the force makes with the horizontal, not the angle that the force makes with the boom.

Edit: What angle does the force make with the boom?

TomHart said:
30 degrees is the angle that the force makes with the horizontal, not the angle that the force makes with the boom.

Edit: What angle does the force make with the boom?
85 degrees.

so I would use the component parallel with the boom, so my answer would be

9800sin(85) * 9 m , correct?

85 degrees.

so I would use the component parallel with the boom, so my answer would be

9800sin(85) * 9 m , correct?
85 degrees is right. That is the angle between the boom and the force. And I believe 9800(sin85)(9) is the correct answer. But that is the perpendicular component, not the parallel component.

## 1. What is a "wrecking ball torque question"?

A "wrecking ball torque question" refers to a physics problem where a wrecking ball is suspended by a cable and used to demolish a building. The question typically involves calculating the torque, or rotational force, required for the ball to swing and hit the building with enough force to cause damage.

## 2. How is torque calculated in a "wrecking ball torque question"?

To calculate torque, you need to know the force applied and the distance from the point of rotation. In a "wrecking ball torque question", the force is the weight of the ball and the distance is the length of the cable. The formula for torque is torque = force x distance.

## 3. What factors affect the torque in a "wrecking ball torque question"?

The torque in a "wrecking ball torque question" is affected by the weight of the ball, the length of the cable, and the angle at which the ball is released. The greater the weight and length of the cable, the greater the torque. The angle at which the ball is released also plays a role in determining the direction and magnitude of the torque.

## 4. How is torque used in real-world applications of "wrecking ball torque questions"?

In real-world applications, torque is used to determine the necessary force and angle for a wrecking ball to successfully demolish a building. It is also used in engineering and construction to calculate the strength and stability of structures, such as bridges and cranes.

## 5. Are there any real-life examples of "wrecking ball torque questions"?

Yes, there are many real-life examples of "wrecking ball torque questions" in the demolition industry. Wrecking balls are commonly used to bring down large structures, such as buildings and bridges. The torque calculations are crucial in ensuring that the ball hits the target with enough force to cause damage and bring down the structure.

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