Chapter 5 - Forces

Question 0

The equation for moment M

Answer 0

M = Fd

Question 1

Moment of a torque

Answer 1

It is the product of the force and the perpendicular distance of the force from the pivot

Question 2

Torque of a couple

Answer 2

It is the product of a magnitude of one force and the perpendicular distance between two forces

Question 3

The equation for torque T

Answer 3

T = Fd

Question 4

Centre of gravity

Answer 4

It is the point at which the whole weight of the body is considered to act

Question 5

Principle of moment

Answer 5

The sum of the clockwise moments about a point equals the sum of the anticlockwise moments about the same point

Question 6

2 conditions for a body to be in equilibrium

Answer 6

1. Resultant force is zero
2. Resultant moment / torque is zero OR
   sum of clockwise moments = sum of anticlockwise moments

Question 7

Describe how to draw a vector triangle to represent forces in equilibrium. Add a confirmation.

Answer 7

1. Each force is represented by an arrow - in magnitude and direction
2. The arrows are joined head to tail
   (Confirmation: If the triangle is ‘closed’, then the forces are in equilibrium)

Question 8

Why a weight couldn’t be supported by strings that are horizontal

Answer 8

1. The forces in strings would be horizontal

2. So, there’s no vertical force to support the weight

Question 9

A card swings on a rod. List 2 forces, other than weight and air resistance, that act on the card during the time it is swinging

Answer 9

1. Normal reaction force at the rod

2. Friction force at the rod

Question 10

State the position in which the cards come to rest. Explain.

Answer 10

The card comes to rest with the weight acting through the rod and allows the centre of gravity to be vertically below the rod.