# Moment vector expression to magnitude of moment

• kleeds
So what is the expression for the magnitude of a vector in terms of its components?In summary, the problem asks for the magnitude and angle of a given moment vector and a force tension vector. The magnitude of the moment vector is given as -2.8i-1.53j+2.24k and the magnitude of the force tension vector is 2.4 kN. The equation for finding the magnitude of a vector is to square all the components, add them, and then take the square root.
kleeds

## Homework Statement

find the magnitude and angle of the moment

moment=-2.8i-1.53j+2.24k

force tension=2.4 kN

rxf=rfsin(theta)

## The Attempt at a Solution

i used the cross product to get i j and k
tried sin and cos of vectors but didnt work.
inverse tan of vectors won't give close to correct angles

Last edited:
Welcome to PF!

As far I as I can tell, the first part of the question is simply asking what the magnitude of the given vector is. You have all three components of the vector.

What is the expression for the magnitude of a vector in terms of its components?

I have no idea. The last time i did vectors at least six months ago.

nevermind you square them all, add them, then take the square root.

kleeds said:
nevermind you square them all, add them, then take the square root.

Yeah.

## 1. What is a moment vector expression?

A moment vector expression is a mathematical representation of the moment of a force or torque acting on a body. It includes both the magnitude and direction of the moment and is typically represented as a vector with a specified point of application.

## 2. How is the magnitude of a moment determined from its vector expression?

The magnitude of a moment can be determined by taking the cross product of the force vector and the position vector, both of which are included in the moment vector expression. The resulting magnitude is measured in units of force multiplied by distance, such as newton-meters.

## 3. Can the direction of a moment be determined from its vector expression?

Yes, the direction of a moment can be determined by the right-hand rule. If the fingers of your right hand wrap around the force vector in the direction of rotation and your thumb points in the direction of the position vector, then the direction of the moment will be perpendicular to both vectors and pointing outwards.

## 4. How does the moment vector expression differ from the moment arm?

The moment vector expression includes both the magnitude and direction of the moment, while the moment arm only represents the distance between the point of application and the axis of rotation. The moment arm is a scalar quantity, whereas the moment vector is a vector quantity.

## 5. Can the moment vector expression be used to calculate the net moment on a body?

Yes, the net moment on a body can be calculated by summing all of the individual moment vectors acting on the body. This can be achieved by breaking down the vector expression into its components and using vector addition to find the resultant moment.

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