Unit 1.1 Basic physics

Question 1

Define quantity.

Answer 1

It is represented by a number multiplied by a unit.

Question 2

Define pressure.

Answer 2

force / area

Question 3

State homogeneity rule 1.

Answer 3

Two quantities “a” and “b” can only be added together if they have the same units- and then the answer has the same units. The same goes for subtraction.

Question 4

State homogeneity rule 2.

Answer 4

An equation is homogeneous only if the units of the two sides are the same.

Question 5

Define scalar quantity.

Answer 5

Has magnitude only.

Question 6

Define vector quantity.

Answer 6

Has magnitude and direction.

Question 7

Define resultant force.

Answer 7

The combined effect of two (or more) forces.

Question 8

Give the symbol for resultant force.

Answer 8

ΣF (‘sigma F’)

Question 9

How would you calculate the sum of 2 forces?

Answer 9

Using the parallelogram law of vector addition.

Question 10

Give 3 ways to find ΣF.

Answer 10

1. Drawing a scale diagram
2. Using trigonometry
3. Pythagoras’ theorem (if the forces are in right angles)

Question 11

Define mean speed.

Answer 11

distance / time

Question 12

Define mean velocity.

Answer 12

displacement / time

Question 13

Define displacement.

Answer 13

A quantity which includes direction as well distance.

Question 14

Give 3 examples of scalar quantities.

Answer 14

1. Density
2. Mass
3. Volume

Question 15

Give 3 examples of vector quantities.

Answer 15

1. Displacement
2. Velocity
3. Acceleration

Question 16

Define resolving.

Answer 16

Finding the component of a force: we resolve a force into its horizontal and vertical components.

Question 17

Give the formula to work out Fₕ (‘horizontal force’).

Answer 17

Fₕ = F cosθ

Question 18

Give the formula to work out Fᵥ (‘vertical force’).

Answer 18

Fᵥ = F sinθ

Question 19

Define density, ρ.

Answer 19

Mass / volume

Question 20

Give unit for density.

Answer 20

kg m⁻³

Question 21

How to convert cm³ into m⁻³ ?

Answer 21

1 cm³ = 1 x 10⁻⁶ m⁻³

Question 22

How to convert kg m⁻³ into g cm⁻³ ?

Answer 22

1000 kg m⁻³ = 1 g cm⁻³

Question 23

Define moment.

Answer 23

The moment of a force about a point is the product of the force and the perpendicular distance from the point to the line of action of the force.

Question 24

Give the units for moment.

Answer 24

Nm

Question 25

Give another name for moment.

Answer 25

Torque

Question 26

Give 2 types of moment.

Answer 26

1. Clockwise moment (CM) 2. Anticlockwise moment (ACM)

Question 27

Give 2 formulas for moment.

Answer 27

1. Force * distance (Fd) 2. F* xcosθ

Question 28

State the principle of moments (PoM).

Answer 28

For a body to be in equilibrium, the sum of the anticlockwise moments about any point is equal to the sum of the clockwise moments about the same point.

Question 29

Give another condition for a body to be in equilibrium.

Answer 29

The resultant moment about any point is zero.

Question 30

What is the centre of gravity?

Answer 30

The point at which we can consider all its weight to act.

Question 31

If an object is moving and rotating at a constant rate, is it in equilibrium?

Answer 31

Yes

Question 32

Give 2 conditions for an equilibrium.

Answer 32

1. The resultant force on the object must be zero. 2. The resultant moment (about any point) must be zero.

Question 33

Give 2 methods to work out 2 unknown forces in a moment question.

Answer 33

1. Resolve once and take moments once. 2. Take moments about 2 different point.