# Why Is My Calculation of Net Torque Incorrect?

• jghlee
In summary, the problem involves calculating the net torque of three forces on a square metal plate pivoted around a center point. After individually calculating the torques for each force and finding the net torque, the answer is incorrect. The mistake is likely multiplying by sin45 instead of dividing by it.
jghlee

## Homework Statement

This is the problem: http://session.masteringphysics.com/prob ...

A squar emetal plate .180 m on each side is pivoted about an axis through point O at its center and perpendicular to the plate. Calculate the net torque about this axis due to the three forces shown in the figure if the magnitudes of the forces are F1=18.0n, F2=26.0N, and F3=14.0N. The plate and all forces are in the plane of the page.

## The Attempt at a Solution

Okay so this problem looks simple enough... but I get the wrong answer.

So here's what I did. I individually calculated the torques for each force.

Torque for F1: (18.0)(.09)=1.62
Torque for F2: (26.0)(.09)=2.34
Torque for F3: (14.0)(sin45)(.09)=.89095

Then I find the net torque by...
-F1+F2+F3=1.61N m

but the answer should be 2.5N m.

Can anybody tell me what I'm doing wrong?

Last edited by a moderator:

Welcome to PF!

jghlee said:
Torque for F1: (18.0)(.09)=1.62
Torque for F2: (26.0)(.09)=2.34
Torque for F3: (14.0)(sin45)(.09)=.89095

Then I find the net torque by...
-F1+F2+F3=1.61N m

but the answer should be 2.5N m.

Hi jghlee! Welcome to PF!

I can't see the picture (you've chopped off the end of the url ) …

but since you're exactly 0.89 out, my guess is that you've multiplied by sin45º instead of dividing by it!

## 1. What is net torque?

Net torque is the overall rotational force acting on an object. It is the sum of all the individual torques exerted on the object.

## 2. How is net torque calculated?

Net torque is calculated by multiplying the force acting on the object by the distance from the axis of rotation to the point of application of the force. This is represented by the equation T = F x r, where T is torque, F is force, and r is the distance.

## 3. What is the unit of measurement for net torque?

Net torque is typically measured in units of newton-meters (N*m) in the SI system or foot-pounds (ft-lb) in the English system.

## 4. How does the direction of the force affect net torque?

The direction of the force affects the direction of the net torque. If the force is applied perpendicular to the radius, the torque will be at its maximum. If the force is applied parallel to the radius, there will be no torque.

## 5. Can you have a net torque of zero?

Yes, if the sum of all the torques acting on an object is zero, the net torque will also be zero. This can occur when the clockwise and counterclockwise torques are equal in magnitude and cancel each other out.

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