Topic 2 - Motion and forces

Question 1

Describe a scalar quantity

Answer 1

A scalar quantity has just magnitude

Question 2

Describe a vector quantity

Answer 2

A vector quantity has both magnitude and a specific direction

Question 3

Explain the difference between vector and scalar quantities

Answer 3

Generally, scalar cannot be negative, but vectors can be, as a certain direction is positive

Question 4

Give examples of vector/scalar quantities

Answer 4

Scalar:
-Speed
-Distance
-Time
-Mass
-Energy

Vector:
-Velocity
-Displacement
-Acceleration
-Force
-Momentum

Question 5

What is the equation for speed?

Answer 5

(average) speed (metre per second, m/s) = distance (metre, m) ÷ time (s)

Question 5

Describe velocity

Answer 5

Velocity is speed in a stated direction

Question 6

What is the equation for distance travelled?

Answer 6

distance travelled (metre, m) = average speed (metre per second, m/s) × time (s)

Question 7

Describe Distance Time graphs

Answer 7

The gradient is velocity.
The sharper the gradient means faster speed.
A negative gradient is returning back to the starting point.
A horizontal line means stationary.
0 distance means that it is back to the starting point.
Curved line means the velocity is changing (acceleration).

Question 8

What is the equation for acceleration?

Answer 8

acceleration (metre per second squared, m/s²) = change in velocity (metre per second, m/s) ÷ time taken (second, s)
a = v-u ÷ t

Question 9

What is the equation which uses change in velocity?

Answer 9

(final velocity)² (m/s)²) – (initial velocity)² (m/s)²) = 2 × acceleration ( m/s²) × distance (metre, m)

v²-u² = 2ax

Question 10

Describe Velocity Time Graphs

Answer 10

Gradient is acceleration.
Sharper gradient means greater acceleration.
Negative gradient is deceleration.
Horizontal line, constant speed.
0 velocity means that it is stationary.
Area under line = distance travelled.
Curved line means that the acceleration is changing.

Question 11

How do you determine constant speeds?

Answer 11

Measure distance travelled.
Use stopwatch for time taken.
Use speed = distance/time

Question 12

How do you determine average speed?

Answer 12

Work out total distance travelled.
Find the time taken for the whole journey.
Use speed = distance/time

Question 13

How do you determine speeds using light gates? Why is this more accurate than other methods?

Answer 13

Set up two, one at start and one at end.
Measure distance between them.
As soon as the object passes through the first, it will measure the time taken to reach the second.
Then use speed = distance/time

This is more accurate as it removes reaction time and human error with a stopwatch.

Question 14

What are the typical speeds for wind, sound, walking, running, cycling, bus, train and plane?

Answer 14

Wind = 5-7ms⎺¹
Sound= 340ms⎺¹
Walking= 5km/h = 1.4ms⎺¹
Running= 6mph = 3ms⎺¹
Cycling= 15km/h = 4ms⎺¹
Bus= 14km/h
Train= 125 miles/h
Plane= 900km/h

Question 14

What is acceleration in freewill?

Answer 14

10m/s²

Question 15

What is Newton’s first law?

Answer 15

An object has a constant velocity unless acted on by a resultant force

Question 16

If a resultant force acts on an object how will it react based on Newton’s first law?

Answer 16

It will accelerate. Acceleration is change in velocity over time so the velocity will change. So the direction or speed of the object will change (or both).

Question 17

If the resultant force is zero how will an object react based on Newton’s first law?

Answer 17

There will be no acceleration so it will move at constant velocity (same speed and direction).
If the object is a rest there is no speed.

Question 18

What is Newton’s second law as an equation?

Answer 18

force (newton, N) = mass (kilogram, kg) × acceleration (metre per second squared, m/s²)
F = m*a

Question 19

What is the equation for weight?

Answer 19

weight (newton, N) = mass (kilogram, kg) × gravitational field strength (newton per kilogram, N/kg)
W = m*g

Question 20

How is weight measured?

Answer 20

Using a force meter, or weighing scales and is used to work out the mass of an unknown object.

Question 21

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

Answer 21

The greater the gravitational field strength, the greater the weight.

Question 22

Describe the core practical to investigate the relationship between force, mass and acceleration by varying the masses added to trolleys

Answer 22

-Cut an interrupt card to a known length (such as 10 cm) and attach it to an air track glider.
-Set up a string attached to the glider with a bench pulley at the end of a tube and a weight hanging down over the pulley. 2 light gates should be on the glider’s path. Attach an air blower (e.g. vacuum). Make sure that the air track is level, and that the card will pass through both gates before the masses strike the floor.
-Set the data logging software to calculate acceleration.
-Use scales to measure the total mass of the glider, string and weight stack. Record this value.
Attach the full weight stack (6 x 10g masses) to the end of the string.
-Make sure the glider is in position and switch on the air blower. The glider should accelerate.
-Remove one weight and attach it to the glider using blu-tack. This will keep the total mass constant. (The weight stack is being accelerated too.)
-Repeat steps 6-7 removing one weight from the stack each time. Remember to attach each weight to the glider as it is removed from the weight stack.

Question 23

What happens when an object is moving in a circle with constant speed?

Answer 23

The speed is constant, but direction always changing so the velocity is always changing. Therefore, it is accelerating.

Question 24

What must there be for motion in a circle?

Answer 24

There must be a force which supplies this acceleration. This is called centripetal free, and is directed/acts towards the centre of the circle.

Question 25

Define inertial mass and explain what it is a measure of.

Answer 25

Inertial mass is a measure of how difficult it is to change the velocity of an object (including from rest) It is defined as the ratio of force over acceleration.

Question 26

What is Newton’s third law?

Answer 26

Every action force has an equal and opposite reaction force.

Question 27

How would you apply Newton’s third law to equilibrium situations and collision interactions?

Answer 27

-The weight of object 1 on object 2 is counteracted by the reaction force of object 2 on object 1
-Momentum is always conserved in a collision (where there are no external forces). Total momentum before = total momentum after

Question 28

What is the equation for momentum?

Answer 28

momentum (kilogram metre per second, kg m/s) = mass (kilogram, kg) × velocity (metre per second, m/s) p = m* v

Question 29

What is Newton’s second law as an equation related to momentum?

Answer 29

force (newton, N) = change in momentum (kilogram metre per second, kg m/s) ÷ time (second, s)

F = mv-mu ÷ t

Question 30

Describe the Ruler Drop Experiment

Answer 30

-Someone else holds a ruler just above your open hand
-They drop it at a random time
-Record the distance from the bottom of the ruler to the point where it was caught
-Average this, and 1cm is 50 millisecond, 2cm 60 milliseconds and so on.
The average human reaction is 0.25 seconds or 250 milliseconds

Question 31

How can you discover the stopping distance of a vehicle?

Answer 31

Find the sum of the thinking distance and the braking distance.
The thinking distance is the time before you react and the braking distance after you react, how long it takes the car to slow down and stop.

Question 32

What might affect the stopping/braking distance of a vehicle?

Answer 32

-The mass of the vehicle
-The speed of the vehicle
the driver’s reaction time
-The state of the vehicle’s brakes
-The state of the road
-The amount of friction between the tyre and the road surface

Question 33

What might affect thinking distance?

Answer 33

-Speed
-Affected by reaction time
-Concentration
-Tiredness
-Distractions
-Influence of drugs/alcohol

Question 33

What are the dangers of large decelerations?

Answer 33

-When in a crash, there is a large deceleration. over a very short time as you stop moving from a high speed.
-As force = mass*acceleration, this are deceleration means a great force is exerted on the car and the passengers. This force can cause injury.

Question 34

Describe the dangers of large decelerating in terms of momentum

Answer 34

-Before the crash, you have a large momentum (due to high velocity)
-After the crash, you have no momentum (as you aren’t moving)
-So force = change in momentum/time so a great force is felt

Question 35

How would you estimate the forces felt on a road?

Answer 35

-Use the equation F=ma
-The average mass of a car is 1500kg

Question 36

How would you estimate the distance required for a road vehicle to stop in an emergency?

Answer 36

For braking distance:
Fd = 1/2mv²
so d = 1/2((mv ²)/F)
For thinking distance distance:
Distance = speedreaction time

Stopping distance = thinking distance + braking distance

Question 37

How would you carry out calculations on work done for a vehicle to stop?

Answer 37

-The work done to stop a vehicle is equal to the initial kinetic energy of the vehicle.
-This is because all the kinetic energy the car had has to be transferred to friction for it to stop
-Braking distance ∝ (initial velocity)² as work done = KE = Fd = 1/2mu²