Chapter 2 Kinematics

Question 1

Define scalar quantities.

Answer 1

Scalar quantities are physical quantities that have magnitude only. Examples include distance, speed and time.

Question 2

Define vector quantities.

Answer 2

Vector quantities are physical quantities that have both magnitude and direction. Examples include displacement, velocity and acceleration.

Question 3

What are the differences between distance and displacement?

Answer 3

Distance:

• The total length covered by a moving object regardless of the direction of motion
• A scalar quantity (i.e. has magnitude only)
• Always increases

Displacement:

• The distance measured in a straight line in a specified direction.
• A vector quantity (i.e. has both magnitude and direction)
• Always measured from a specific reference point
• Can be positive or negative, depending on the position of the object from the reference point

Question 4

Define speed.

Answer 4

Speed is the distance moved per unit time.

Question 5

Define instantaneous speed.

Answer 5

The speed of an object at a particular instant.

Question 6

Define velocity.

Answer 6

Velocity is the rate of change of displacement.

Question 7

Define average speed and the assumption made to calculate it.

Answer 7

Average speed is the total distance travelled per unit time. Assume that the object travels at the same speed throughout the entire distance.

Question 8

Define average velocity and the assumption made to calculate it.

Answer 8

Average velocity is the total displacement travelled per unit time. Assume that the object travels at the same velocity throughout the entire journey.

Question 9

Define acceleration.

Answer 9

Acceleration is the rate of change of velocity.

Question 10

When does an object undergo deceleration?

Answer 10

When the velocity of an object decreases over time, it undergoes deceleration.

Question 11

Define uniform acceleration.

Answer 11

Uniform acceleration is the constant rate of change of velocity.

Question 12

When does an object undergo uniform acceleration?

Answer 12

An object undergoes uniform acceleration when the change (increase/ decrease) in its velocity for every unit of time is the same, i.e. the rate of change of velocity is constant.

Question 13

When does an object undergo non-uniform acceleration?

Answer 13

An object undergoes non-uniform acceleration if the change in its velocity for every unit of time is not the same.

Question 14

How do we calculate the total displacement using a velocity-time graph?

Answer 14

Calculate the total area under the velocity-time graph, which gives the total displacement

Question 15

Describe speed in the following scenarios:

1) +ve velocity, +ve acceleration
2) +ve velocity, -ve acceleration
3) -ve velocity, -ve acceleration
4) -ve velocity, +ve acceleration

Answer 15

1) Speeding up in the positive direction (e.g. speeding up while running)
2) Slowing down to zero speed (e.g. slowing down to stop at a red light)
3) Speeding up in the negative direction (e.g. dropping an object from a height, taking upwards as positive)
4) Slowing down to zero speed

Question 16

Explain:

1) Positive acceleration
2) Negative acceleration
3) Deceleration

Answer 16

1) Acceleration in the positive direction
2) Acceleration in the negative direction
3) Negative acceleration with decreasing speed

Question 17

a) Displacement-time graph with constant gradient gives: __________
b) Displacement-time graph with non-uniform gradient gives: __________

Answer 17

1) Displacement-time graph with constant gradient gives velocity of the object
b) Displacement-time graph with non-uniform gradient: gradient of tangent is equal to the instantaneous velocity of the object at that instant

Question 18

Given a speed-time graph, what does the area under the graph give?

Answer 18

Area under speed-time graph = distance travelled by object

Question 19

Negative gradient = object moving towards observer

True or false?

Answer 19

False.

Negative gradient ≠ object moving towards observer.

Displacement approaching zero either from +ve or -ve direction = object moving towards observer

Question 20

Given a velocity-time graph, what does the

a) Gradient
b) Area under graph

give?

Answer 20

a) Gradient of the velocity-time graph = acceleration of the object.
b) Area under the velocity-time graph = total displacement of the object

Question 21

a) Velocity-time graph with constant gradient gives: __________
b) Velocity-time graph with non-uniform gradient gives: __________

Answer 21

a) Velocity-time graph with constant gradient gives acceleration of the object
b) Velocity-time graph with non-uniform gradient: gradient of tangent is equal to the instantaneous acceleration of the object at that instant

Question 22

What is the acceleration due to gravity?

Answer 22

It is a constant that is approximately 10 m/s² (i.e. steadily increasing velocity)

Question 23

When does an object experience acceleration due to gravity?

Answer 23

When does an object experience acceleration due to gravity?

Question 24

What is free-fall?

Answer 24

Free-fall is the motion of objects that move under the sole influence of gravity; free-falling objects do not encounter air resistance.

Question 25

What is the relationship of air resistance with:

1) Motion of moving objects
2) Speed of objects
3) Surface area of objects
4) Density of air

Answer 25

1) Opposes the motion of moving objects
2) Increases with speed of objects
3) Increases with surface area of objects
4) Increases with the density of air