Topic 2 - Forces And Motion

Question 1

Scalar vs Vector

Answer 1

• A scalar quantity only has a magnitude
• A vector quantity has both a magnitude and a direction

Question 2

How do vector arrows represent vectors?

Answer 2

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

Question 3

Examples of vector quantities

Answer 3

1. Velocity
2. Displacement
3. Force

Question 4

6 examples of scalar quantities

Answer 4

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

Question 5

Definition of velocity

Answer 5

The speed of an object in a specific direction

Question 6

What does the gradient represent on a distance-time graph?

Answer 6

The speed.

Question 7

On a displacement-time graph, what does the gradient represent?

Answer 7

The velocity.

Question 8

How to calculate the speed at a given time for a distance-time graph for an accelerating object?

Answer 8

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

Question 9

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

Answer 9

• Calculate the area under the graph

Question 10

On a velocity-time graph, what does the gradient represent?

Answer 10

The acceleration.

Question 11

Speed of sound

Answer 11

330 m/s

Question 12

Human walking speed

Answer 12

1.5 m/s

Question 13

Human running speed

Answer 13

3 m/s

Question 14

Human cycling speed

Answer 14

6 m/s

Question 15

Gravity strength on Earth

Answer 15

10 m/s^2

Question 16

Define resultant force:

Answer 16

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

Question 17

Newton’s First Law for a stationary object:

Answer 17

If the resultant force on a stationary object is zero, the object will remain at rest.

Question 18

Newton’s first law for a moving object

Answer 18

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

Question 19

Newton’s Second Law in words

Answer 19

• An object’s acceleration is directly proportional to the resultant force acting on it.
• And inversely proportional to its mass.

Question 20

What is weight?

Answer 20

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

Question 21

Unit for gravitational field strength

Answer 21

N/kg

Question 22

What piece of equipment can measure an object’s weight?

Answer 22

• A calibrated spring-balance
• A newton meter

Question 23

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

Answer 23

• When the object is changing direction
• For example, moving in a circle

Question 24

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

Answer 24

• Speed is scalar
• 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
• The velocity is therefore constantly changing

Question 25

The resultant force that acts on an object moving in a circle and its direction

Answer 25

- Centripetal force - Acts towards the centre of the circle

Question 26

What is inertial mass?

Answer 26

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

Question 27

State Newton’s Third Law

Answer 27

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

Question 28

Unit for momentum

Answer 28

kg m/s

Question 29

In a closed system, what can be said about the momentum before and after a collision?

Answer 29

The total momentum before and after are equal.

Question 30

How to measure human reaction times:

Answer 30

- Using a ruler drop test, where: - 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 31

Why does the 0cm mark need to be at the bottom in the ruler drop test?

Answer 31

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

Question 32

What is the stopping distance of a vehicle equal to?

Answer 32

The sum of the thinking distance and the braking distance.

Question 33

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

Answer 33

The stopping distance increases

Question 34

Range of values of human reaction time

Answer 34

0.2 to 0.9 s

Question 35

Factors affecting a driver’s reaction time

Answer 35

1. Tiredness 2. Drugs 3. Alcohol

Question 36

Factors affecting braking distance

Answer 36

1. Adverse (wet/icy) road conditions 2. Poor tyre/brake conditions

Question 37

Describe the energy transfers that take place when a car applies its brakes (4 marks)

Answer 37

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

Question 38

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

Answer 38

It also increases.

Question 39

Two consequences of a vehicle undergoing very large decelerations:

Answer 39

- The amount of kinetic energy converted to heat is very high causing breakers to overheat. - Loss of control of the vehicle