Topic 2: Mechanics

Question 1

Define scalars.

Answer 1

Quantities with only a magnitude (size) eg. temperature, distance.

Question 2

Define vectors.

Answer 2

Quantities with both magnitude and direction eg. displacement.

Question 3

Define distance (d).

Answer 3

How far you have travelled. Measured in metres (m).

Question 4

Define displacement (s).

Answer 4

The distance travelled in a particular direction. Measured in metres (m).

Question 5

Define speed.

Answer 5

The rate of change of distance (distance divided by time). Measured in ms⁻¹.

Question 6

Define velocity.

Answer 6

The rate of change of displacement (displacement divided by time). Measured in ms⁻¹.

Initial velocity = u
Final velocity = v

Question 7

Define instantaneous speed.

Answer 7

The rate of change of distance at one particular time.

Question 8

Define average speed.

Answer 8

The speed over a period of time (the total distance divided by the total time).

Question 9

Define acceleration (a).

Answer 9

The rate of change of velocity (change in velocity divided by time). Measured in ms⁻².

Question 10

When do the equations of motion given in the data booklet apply?

Answer 10

When the object is accelerating at a constant rate (uniform acceleration).

Question 11

What is the gradient of displacement-time graphs?

Answer 11

In displacement-time graphs the gradient is the velocity (as velocity is the rate of change of displacement over time).

Question 12

What is the gradient of velocity-time graphs?

Answer 12

In velocity-time graphs the gradient is the acceleration (as acceleration is the change of velocity divided by time).

The area below the line is the displacement.

Question 13

What is the gradient of acceleration-time graphs?

Answer 13

Acceleration. The area below the line is the change in velocity.

Question 14

Define a projectile.

Answer 14

An object moving through the air under the influence of only one force - gravity. The trajectory it will follow is a parabola.

Question 15

Why is the path a projectile will take a parabola?

Answer 15

Because the vertical component of the velocity is constantly changing (due to the force of gravity) and the horizontal component of the velocity is constant (assuming no air resistance).

Question 16

In reality, why will the trajectory of a projectile not be a parabola?

Answer 16

Because of air resistance. This will cause a shorter range, a lower max and a steeper gradient on the way down (i.e. the trajectory is not symmetric).

Question 17

When is vertical and horizontal motion considered in projectile problems?

Answer 17

Vertical motion is considered when calculating the maximum height reached or the time of the flight. Horizontal motion is considered when calculating the range of the projectile.

Question 18

Give the formula to find the range in projectile problems.

Answer 18

Range = horizontal velocity x time

Question 19

Give the formula to find the initial velocity in projectile problems.

Answer 19

Initial velocity = √ Vh² + Vv²

Question 20

Give the initial vertical velocity and horizontal velocity for projectiles launched horizontally.

Answer 20

Initial vertical velocity: zero
Horizontal velocity: launch velocity, v

Question 21

Give the initial vertical velocity and horizontal velocity for projectiles launched at an angle above the horizontal.

Answer 21

Initial vertical velocity: vsinθ
Horizontal velocity: vcosθ

Question 22

Give the initial vertical velocity and horizontal velocity for projectiles launched at an angle below the horizontal.

Answer 22

Initial vertical velocity: vsinθ
Horizontal velocity: vcosθ

Question 23

What does the magnitude of fluid resistance depend on?

Answer 23

• The velocity of the object relative to the fluid
• The size and shape of the object
• The fluid used (its viscosity)

Question 24

What is terminal velocity?

Answer 24

When the magnitude of the upwards air resistance is equal to the downwards gravitational force (weight) the object will no longer accelerate because the forces of the object are balanced. Its speed would remain constant, and this specific speed is called terminal velocity.

Question 25

Define mass.

Answer 25

The amount of matter in an object (m). Measured in kilograms (kg). It does not change with a change in position.

Question 26

Define weight.

Answer 26

The force of gravity acting on an object. Measured in newtons (N). It changes if an object changes its position.

Question 27

Give Newton’s First Law (Law of Inertia).

Answer 27

An object continues in uniform motion in a straight line or at rest unless a resultant external force acts.

Question 28

What is translational equilibrium?

Answer 28

If the resultant force on the object is zero, it is not accelerating and is said to be in translational equilibrium.

Question 29

Give Newton’s Second Law.

Answer 29

The resultant force on an object is proportional to the acceleration providing the mass of the object remains constant. F = ma

Question 30

Give Newton’s Third Law.

Answer 30

For every action on one object there is an equal but opposite reaction on another object.

Question 31

When the weight force on a slope is resolved into two forces what are they?

Answer 31

Parallel to a slope: mgsinθ
Perpendicular to a slope: mgcosθ

Question 32

What are the two types of solid friction?

Answer 32

Static friction: occurs when there is no relative motion between the surfaces.
Dynamic (kinetic) friction: occurs when there is relative motion between the surfaces.

Question 33

Define energy (E).

Answer 33

The capacity to do work. Measured in joules (J).

Question 34

Define work (W).

Answer 34

A transfer of energy. Measured in joules (J).

Question 35

Define power (P).

Answer 35

The rate at which work is done or energy is transferred. Measured in watts (W).

Question 36

Give the law of conservation of momentum.

Answer 36

The total linear momentum of a system remains constant provided no resultant external force acts.

Question 37

Define linear momentum (p).

Answer 37

The product of mass and velocity. It is a vector. Measured in kgms⁻¹ or Ns.

Question 38

Give the initial vertical velocity and horizontal velocity for projectiles launched at an angle below the horizontal.

Answer 38

Initial vertical velocity: vsinθ
Horizontal velocity: vcosθ

Question 39

What happens during an elastic collision?

Answer 39

No kinetic energy is lost. The total amount of energy remains constant. Momentum is conserved.

Question 40

What happens during an inelastic collision?

Answer 40

Kinetic energy is lost. The total amount of energy remains constant. Momentum is conserved.