2. Motion and Forces

Question 1

What is a scalar quantity?

Answer 1

• A quantity that only has a magnitude.
• A quantity that isn’t direction dependent.

Question 2

What is a vector quantity?

Answer 2

A quantity that has both a magnitude and an associated direction.

Question 3

How can a vector quantity be drawn?

Answer 3

Using vector arrows.

Question 4

How do vector arrows represent vectors?

Answer 4

• The length of the arrow represents the magnitude.
• The arrow points in the associated direction.

Question 5

Give examples of vector quantities

Answer 5

• Velocity
• Displacement
• Force
• Acceleration
• Weight
• Momentum

Question 6

Give examples of scalar quantities

Answer 6

• Temperature
• Time
• Mass
• Speed
• Distance
• Energy

Question 7

What is velocity?

Answer 7

The speed of an object in a specific direction.

Question 8

Give an equation relating average speed, distance and time.

Answer 8

average speed = distance / time

Question 9

On a distance/time graph, what value does the gradient of the line represent?

Answer 9

The speed.

Question 10

On a displacement/time graph, what value does the gradient of the line represent?

Answer 10

The velocity.

Question 11

What must be done to calculate speed at a given time from a distance-time graph for an accelerating object?

Answer 11

• Draw a tangent to the curve at the required time.
• Calculate the gradient of the tangent.

Question 12

How can the distance travelled by an object be calculated from a velocity-time graph

Answer 12

It is equal to the area under the graph.

Question 13

On a velocity/time graph what does the gradient of the line represent?

Answer 13

The acceleration.

Question 14

State a typical value for the speed of sound

Answer 14

340 m/s

Question 15

What is a typical value for human walking speed?

Answer 15

1.4 m/s

Question 16

What is a typical value for human running speed?

Answer 16

3 m/s

Question 17

What is a typical value for human cycling speed?

Answer 17

6 m/s

Question 18

Give an appropriate value for the acceleration of an object in free fall under gravity near the Earth’s surface.

Answer 18

10 m/s²

Question 19

What is displacement?

Answer 19

A vector quantity which measures the distance and the direction in a straight line from an object’s starting point to its finishing point.

Question 20

What is acceleration?

Answer 20

The change in velocity in a certain amount of time.

Question 21

What is the name given to the single force that is equivalent to all the other forces acting on a given object?

Answer 21

The resultant force.

Question 22

What is Newton’s First Law for a stationary object?

Answer 22

If the resultant force on a stationary object is zero, the object doesn’t move.

Question 23

What is Newton’s First Law for a moving object?

Answer 23

If the resultant force on a moving object is zero, the object will remain at constant velocity (same speed in same direction).

Question 24

State the defining equation for Newton’s Second Law

Answer 24

Resultant force = mass x acceleration

F = ma

Question 25

What is Newton's Second Law in words?

Answer 25

An object's acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass.

Question 26

What is weight?

Answer 26

The force that acts on an object due to gravity and the object's mass.

Question 27

What quantities does weight depend on?

Answer 27

Weight = mass x gravitational field strength - The object's mass - The gravitational field strength at the given position in the field.

Question 28

What is the unit used for weight?

Answer 28

Newton (N)

Question 29

What is the unit used for gravitational field strength?

Answer 29

N/kg

Question 30

What piece of equipment can be used to measure an object's weight?

Answer 30

A calibrated spring-balance or newton-meter.

Question 31

When can an object travelling at a constant speed not have a constant velocity?

Answer 31

When the object is changing direction; for example, moving in a circle.

Question 32

Why does an object travelling at a constant speed in a circle not have a constant velocity?

Answer 32

- Speed is a scalar quantity. - Velocity is a vector quantity which means it can only be constant if the direction is constant. - In circular motion, the direction is continuously changing. - Therefore velocity is constantly changing.

Question 33

What is the resultant force that acts on an object moving in a circle called, and in which direction does it act?

Answer 33

It is called the centripetal force and acts towards the centre of the circle.

Question 34

What is inertial mass?

Answer 34

- A measure of how difficult it is to change a given object's velocity. - The ratio of force over acceleration.

Question 35

State Newton's Third Law

Answer 35

Whenever two objects interact, the forces that they exert on each other are always equal and opposite.

Question 36

State the equation used to calculate an object's momentum.

Answer 36

Momentum = mass x velocity

Question 37

What is the unit used for momentum?

Answer 37

kgm/s kilogram metres per second

Question 38

What is conservation of momentum?

Answer 38

In a closed system, the total momentum before and after are equal.

Question 39

How can you measure human reaction times?

Answer 39

- Using the ruler drop test. - Person A and B hold each end of a ruler with the 0cm mark at the bottom. - Person A drops the ruler without telling Person B. - Person B catches it. - The distance travelled corresponds to their reaction time.

Question 40

In the ruler drop test, why is it important that the 0cm mark is at the bottom?

Answer 40

So you can obtain the distance directly without having to calculate it; otherwise, a zero error would need to be accounted for.

Question 41

What is the stopping distance of a vehicle equal to?

Answer 41

The sum of thinking distance and braking distance.

Question 42

For a given braking distance, if the vehicle's speed is increased, what can be said about its stopping distance?

Answer 42

The stopping distance is increased with an increase in speed.

Question 43

Give a typical range of values for human reaction time.

Answer 43

0.2 seconds - 0.9 seconds

Question 44

Give three factors which can affect a driver's reaction time.

Answer 44

- Tiredness - Drugs/alcohol - Distractions (such as noise)

Question 45

Factors which may increase braking distance.

Answer 45

- Faster vehicle speed - Poor, wet, or icy road surface conditions - Damaged or worn brakes or tyres conditions.

Question 46

Factors which may increase thinking distance.

Answer 46

- Faster vehicle speed - Long driver reaction times

Question 47

What is thinking distance?

Answer 47

How far a vehicle moves during driver's reaction time.

Question 48

What is braking distance?

Answer 48

The distance taken to stop whilst brakes are applied.

Question 49

Describe the energy transfers that take place when a car applies its brakes.

Answer 49

- Work is done by the friction force between the brakes and wheel. - Kinetic energy of the wheel is converted to heat and is dissipated to the surroundings through the brake discs.

Question 50

To stop a car in a given distance, if its velocity is increased, what must happen to the braking force applied?

Answer 50

The braking force must also be increased.

Question 51

State two consequences of a vehicle undergoing very large decelerations.

Answer 51

- Kinetic energy converted to heat is very high causing brakes to overheat. - Loss of control of the vehicle, causing it to skid.