Topic 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 represented ?

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 3 examples of vector quantities

Answer 5

• Velocity
• Displacement
• Force

Question 6

Give examples of scalar quantities

Answer 6

• temperature
• mass
• time
• speed
• distance
• energy

Question 7

What is velocity ?

Answer 7

The speed of an object in a specific direction

Question 8

Give an equation linking 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 does the gradient of the line represent ?

Answer 10

The velocity

Question 11

How do you 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

State the equation for the average acceleration of an object. Give appropriate units

Answer 12

Acceleration = change in velocity / time taken

a = m/s^2. V = m/s. t = s

Question 13

Give an equation linking final velocity with initial velocity , displacement and acceleration

Answer 13

V^2 = u^2 + 2as

Question 14

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

Answer 14

It is equal to the area under the graph

Question 15

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

Answer 15

The acceleration.

Question 16

State a typical value for the speed of sound

Answer 16

330 m/s

Question 17

What is a typical value for human walking speed?

Answer 17

1.5 m/s

Question 18

What is a typical value for human running speed?

Answer 18

3m/s

Question 19

What is a typical value for human cycling speed?

Answer 19

6m/s

Question 20

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

Answer 20

10 m/s ^2

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

State Newton’s first law for a stationary object

Answer 22

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

Question 23

State 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

State Newton’s second law

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 A newton metre

Question 31

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

Answer 31

When the object is changing direction E.g 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 - velocity is constantly changing

Question 33

What is the resultant force that acts on an object moving in a circle called, and I’m 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 2 objects interact, the forces that they exert on each other are always equal and opposite

Question 36

Equation for momentum

Answer 36

Momentum = Mass x velocity

Question 37

What unit is used for momentum ?

Answer 37

kgm / s

Question 38

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

Answer 38

The total momentum before and after are equal

Question 39

Equation linking change in momentum , force and time

Answer 39

Force x time = change in momentum

Question 40

How can you measure human reaction times?

Answer 40

Ruler drop test - person A and B hold 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 41

What is the stopping distance of a vehicle equal to?

Answer 41

Thinking distance + braking distance

Question 42

For a given braking distance, if the vehicles 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 times

Answer 43

0.2-0.9 s

Question 44

3 factors which can affect reaction time

Answer 44

Tiredness Drugs Alcohol

Question 45

2 factors which may affect braking distance

Answer 45

Adverse ( wet/icy) road conditions Poor tyre or brake conditions

Question 46

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

Answer 46

- 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 47

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

Answer 47

The braking force must also be increased

Question 48

Two consequences of a vehicle undergoing very large decelerations

Answer 48

- kinetic energy converted to heat is very high causing brakes to overheat - loss of control of vehicle