Scalars & Vectors, Moments + Forces

Question 1

What is a scalar quantity? Give three examples.

Answer 1

→ magnitude only

→ mass, speed & distance

Question 2

What is a vector quantity? Give three examples.

Answer 2

→ magnitude & direction

→ velocity, displacement & acceleration

Question 3

What is displacement?

Answer 3

→ how far away an object is from its original position

→ can be -ive or +ive

Question 4

How do you calculate the resultant vector for:

• parallel vectors in the same direction?
• parallel vectors in the opposite direction?

Answer 4

→ addition

→ subtraction (in the direction of the larger vector)

Question 5

How do you calculate the resultant of two vectors at 90 degrees?

Answer 5

Pythagoras’ Theorem

Question 6

How do you calculate the resultant of two vectors at non-right angle angles?

Answer 6

→ draw a parallelogram
→ draw in the diagonal
→ use scale drawing to measure the diagonal

Question 7

How do you resolve a vector into its horizontal and vertical components? State the mnemonic.

Answer 7

horizontal → Fcosθ
vertical → Fsinθ
‘turn away from your sins’

Question 8

State the conditions required for equilibrium.

Answer 8

→ sum of the forces must equal zero

→ sum of the moments must equal to zero

Question 9

What may be the resultant forces of three coplanar forces?

Answer 9

→ may be zero if object is in equilibrium

→ may be the sum of the 3 forces if they are all acting in the same direction

Question 10

What are the three ways of determining if an object with three forces acting on it is in equilibrium?

Answer 10

1. the resultant of any two of the forces will be equal & opposite to the third
2. the three forces will make a closed triangle
3. → the sum of the horizontal components will be 0
   → the sum of the vertical components will be 0

Question 11

State the principle of moments.

Answer 11

For a system to be in equilibrium, the sum of clockwise moments about a point must be equal to the sum of the anticlockwise moments

Question 12

State what is meant by a couple.

Answer 12

→ pair of equal & opposite coplanar forces that acts to produce rotation only
→ act perpendicular to the distance between them

Question 13

State what is meant by the lift force.

Answer 13

→ an upwards force caused on an object moving through fluid
→ caused by change in direction of the fluid

Question 14

State Newton’s first law of motion.

Answer 14

an object will continue moving at constant velocity or stay at rest unless acted upon by a resultant force