Question Video: Finding the Moment of a Couple Equivalent to a System of Two Forces Acting on a Regular Hexagon | Nagwa Question Video: Finding the Moment of a Couple Equivalent to a System of Two Forces Acting on a Regular Hexagon | Nagwa

# Question Video: Finding the Moment of a Couple Equivalent to a System of Two Forces Acting on a Regular Hexagon Mathematics • Third Year of Secondary School

## Join Nagwa Classes

π΄π΅πΆπ·π»π is a regular hexagon with sides of length 5 cm. Two forces of the same magnitude 13 N are acting along πΆπ΅ and ππ» respectively. Determine the magnitude of the moment of the couple.

03:19

### Video Transcript

π΄π΅πΆπ·π»π is a regular hexagon with sides of length five centimeters. Two forces of the same magnitude 13 newtons are acting along πΆπ΅ and ππ», respectively. Determine the magnitude of the moment of the couple.

We will begin by sketching the regular hexagon as shown. We are told that it has side length five centimeters. There are two forces of magnitude 13 newtons acting along πΆπ΅ and ππ», respectively. These two forces form a couple, as they are a pair of parallel forces with equal magnitude and opposite direction which do not lie on the same line of action. We are asked to calculate the magnitude of the moment of this couple.

This is equal to πΉπ sin π, where πΉ is the magnitude of the forces β in this question, 13 newtons β π is the distance between their points of action β in this case, the line segment ππΆ β and π is the angle that the forces make with this line segment. If we let the center of the hexagon be point π, we can use our properties of hexagons to help determine the length of ππΆ and the angle π. The line segment π΄π΅ is parallel and equal in length to the line segment ππΆ. This means that ππΆ is equal to five centimeters. Likewise, the line segment π»π· is the same length and parallel to the line segment ππ. This is also equal to five centimeters, meaning that the line segment ππΆ is equal to 10 centimeters.

Triangle πππ» is therefore equilateral. And we know that the angles in an equilateral triangle equal 60 degrees. The measure of angle π is therefore equal to 60 degrees. And since the two forces form a couple, this is also true of the angle π΅πΆπ. We now have values of πΉ, π, and π. The magnitude of the moment of the couple is equal to 13 multiplied by 10 multiplied by the sin of 60 degrees. Since the sin of 60 degrees is root three over two, this simplifies to 130 multiplied by root three over two, which in turn is equal to 65 root three.

The magnitude of the moment of the couple is therefore equal to 65 root three newton-centimeters.

## Join Nagwa Classes

Attend live sessions on Nagwa Classes to boost your learning with guidance and advice from an expert teacher!

• Interactive Sessions
• Chat & Messaging
• Realistic Exam Questions