Topic 2 - Motion And Forces

Question 1

What is a vector quantity?

Answer 1

Vectors have magnitude and direction

Question 2

Give examples of vector quantities.(6)

Answer 2

Forces, velocity, displacement, weight, acceleration, momentum, etc.

Question 3

What are scalar quantities?

Answer 3

Scalar quantities only have magnitude and no direction.

Question 4

Give example of scalar quantities. (6)

Answer 4

Speed, distance, mass, energy, temperature, time, etc.

Question 5

What is displacement?

Answer 5

Displacement is a vector quantity which measures the distance and the direction in a straight line form the starting point to the finishing point.

Question 6

How is velocity different from speed?

Answer 6

Velocity is speed in a given direction.

Question 7

What is the formula for average speed?

Answer 7

Average speed (m/s)= distance (m) / time (s)

Question 8

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

Answer 8

Speed of an object.

Question 9

Recall typical speeds of these:

• Wind
• Sound in air
• Person walking
• Person running
• Cyclist
• Car driving through town
• Car driving on Motorway
• Train

Answer 9

• Wind - 6m/s
• Sound in the air - 340m/s
• Person walking - 1 m/s
• Person running - 3 m/s
• Cyclist- 5.5 m/s
• Car driving through town - 13 m/s
• Car on Motorway - 30 m/s
• Train - 45 m/s

Question 10

List two equations to work out acceleration.

Answer 10

Acceleration (m/s2)= (V - U) / T (Secs)

v2 - u2 = 2 X a (m/s2) X x(metre)

Question 11

What does a flat line on a distance-time graph represent?

Answer 11

Not moving/stationary

Question 11

What does a diagonal line (/) represent on a distance-time graph?

Answer 11

Moving slowly/quickly (depending on the gradient) at a constant speed.

Question 12

What does a curved line going upwards represent?

Answer 12

Acceleration

Question 12

How do you calculate speed or distance on a point on a curved line on a distance-time graph?

Answer 12

Draw tangent to the curve at the point. Then calculate the gradient of the tangent

Question 13

What is the acceleration in free fall?

Answer 13

10m/s2

Question 13

What is uniform acceleration also known as?

Answer 13

Constant acceleration

Question 14

What does a flat line on a velocity-time graph represent?

Answer 14

Constant velocity

Question 14

What does a -acceleration mean?

Answer 14

Deceleration

Question 15

What does the flat along 0 for the time axis mean (velocity-time graph)?

Answer 15

Stationary

Question 16

How do you find the distance travelled on a velocity-time graph?

Answer 16

Work out area under the line on the graph and above the horizontal axis.

Question 16

How do you work out acceleration from a velocity-time graph?

Answer 16

Acceleration = Gradient of velocity-time graph

Question 17

What is Newton’s first law?

Answer 17

If there is no forces acting on a body (or the forces acting on it are balanced) the object will continue to do what is it is already doing.

• if the object is stationary, it will remain
• if the object is moving, it will continue to move at the same speed and in the same direction

Question 17

What does a diagonal line mean on a velocity-time graph?

Answer 17

Constant acceleration

Question 18

Why does a object moving in a circular motion have a changing velocity?

Answer 18

When an object moves in a circle at a constant speed, its direction constantly changes. A change in direction causes a change in velocity. This is because velocity is a vector quantity – it has an associated direction as well as a magnitude. A change in velocity results in acceleration, so an object moving in a circle is accelerating even though its speed may be constant.

Question 19

Why must there be a centripetal force for circular motion?

Answer 19

An object will only accelerate if a resultant force acts on it. For an object moving in a circle, this resultant force is the centripetal force that acts towards the middle of the circle.

Question 20

Formula for weight (N)

Answer 20

Weight (N) = Mass (kg) x gravitational field strength (n/kg)

Question 21

What is weight measured in?

Answer 21

Newtons

Question 22

Describe the relationship between the weight of a body and the gravitational field strength

Answer 22

Weight is the result of gravity. The gravitational field strength of the Earth is 10 N/kg (ten newtons per kilogram). This means an object with a mass of 1kg would be attracted towards the centre of the Earth by a force of 10N. We feel forces like this as weight.

Question 23

What is Newton’s second law?

Answer 23

The second law states that the acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object. This means that F = M x A

Question 24

What is inertial mass?

Answer 24

The ratio of force over acceleration is called inertial mass. Inertial mass is a measure of how difficult it is to change the velocity of an object.

Question 25

What is Newton’s third law?

Answer 25

For every action, there is an equal and opposite reaction.

Question 27

Describe the Core Practical : Investigate the relationship between force, mass and acceleration by varying the masses added to trolleys

Answer 27

By releasing masses over the side of the bench a force will be applied to the trolley, causing it to accelerate down the ramp. Light gates can be positioned along the ramp to measure the velocity of the trolley at different points and record the time between these measurements. Different number of masses can be added to the trolley.

Question 29

How do you work out momentum?

Answer 29

Momentum (Kgm/s) = Mass (kg) x Velocity (m/s)

Question 30

How do you work out force using momentum?

Answer 30

Force (N) = change in momentum (kgm/s) / time (s)

Question 30

How do you work out the stopping distance?

Answer 30

Thinking distance + Braking distance

Question 30

Which six factors affects stopping distance?

Answer 30

- Mass of Vehicle - Speed of Vehicle - Driver’s reaction time - State of Vehicle’s brakes - State of the road - Amount of friction between tyre and road surface

Question 32

What factors affect Driver’s reaction times?

Answer 32

- Age - Gender - Physical fitness - Fatigue - Distraction - Alcohol

Question 34

Estimate how the distance required for a road vehicle to stop in an emergency varies over a range of typical speeds

Answer 34

``` 20 mph - 12m 30 mph - 23m 40 mph - 36m 50 mph - 53m 60 mph - 73m 70 mph - 96m ```

Question 36

How does Newton’s third law connect to equilibrium situations?

Answer 36

It applies in static (non-moving) situations, such as a book resting on a table. This is where the force from the weight of book and the reaction from the table is equal therefore cancelling out so it doesn’t move.

Question 38

How does Newton’a third law apply to car collisions?

Answer 38

Newton’s Third Law of Motion applies in collisions, such as a car crashing into a tree. The car and tree exert equal and opposite forces on each other in the collision. When two objects collide the total momentum before the collision is equal to the total momentum in the absence of external forces. This is the law of conservation of momentum, it is true for all collisions.

Question 40

How do you work out ‘Work Done’?

Answer 40

Work done = Energy transferred Work (Joules) = Force (Newtons) x Distance moved in direction of force (metres)

Question 42

How do you work out ‘Kinetic Energy’?

Answer 42

Kinetic Energy = 1/2 x mass x velocity squared

Question 43

What does Kinetic Energy equal when stopping a car?

Answer 43

KE = Work done 1/2 x mass x velocity squared = Force (applied by brakes) x Braking distance.

Question 44

Why are large decelerations bad?

Answer 44

When there is a car crash, the car, its contents and the passengers decelerate rapidly. They experience great forces because of the change in momentum which can cause injuries.

Question 45

What safety features are implemented into cars to reduce injury from large decelerations?

Answer 45

Modern cars have safety features that absorb kinetic energy in collisions. These typically include: - seat belts - air bags - crumple zones

Question 46

How do safety features in a car prevent injury to the occupants?

Answer 46

These features reduce injuries to the people in the car by absorbing energy from the impact. They increase the time taken for the change in momentum on the occupants' bodies, and so reduce the forces involved and any subsequent injuries.