Describing motion along a line (5.6.1) (M)

Question 1

What is distance?

Answer 1

how far an object moves

Question 2

What type of quantity is distance?

Answer 2

scalar - does not involve direction

Question 3

What is displacement?

Answer 3

A measure that includes both the distance an object moves, measured in a straight line from the start point to the finish point and the direction of that straight line

Question 4

What type of quantity is displacement?

Answer 4

vector

Question 5

What type of quantity is speed?

Answer 5

scalar - does not involve direction

Question 6

The speed of a moving object is (…) constant. When people walk, run or travel in a car their speed is (…)

Answer 6

rarely

constantly changing

Question 7

4 needed

What are some factors that can affect the speed at which a person can walk, run or cycle

Answer 7

• age
• terrain
• fitness
• distance travelled

Question 8

What is the typical speed of walking?

Answer 8

∼ 1.5 m/s

Question 9

What is the typical speed of running?

Answer 9

∼ 3.0m/s

Question 10

What is the typical speed of cycling?

Answer 10

∼ 6.0m/s

Question 11

What are the typical speeds of a car, train and aeroplane?

Answer 11

car - 13/30m/s

train - 50m/s

aeroplane - 250m/s

Question 12

Do the speed of sound and the speed of the wind vary or stay the same?

Answer 12

vary

Question 13

What is the typical value for the speed of sound in air?

Answer 13

330m/s

Question 14

What is the velocity of an object?

Answer 14

its speed in a given direction

Question 15

What type of quantity is velocity?

Answer 15

vector

Question 16

How can something in a circular motion (e.g. satellites), have constant speed but have changing velocity?

Answer 16

If something is in circular motion, its direction is constantly changing

Question 17

How can the speed of an object e calculated from a distance-time graph?

Answer 17

Calculate the gradient

Question 18

How can speed at any particular time be determined from a distance-time graph?

Answer 18

by drawing a tangent at that point and measuring the gradient

Question 19

What is acceleration?

Answer 19

the rate of change of velocity

Question 20

How would you describe an object that is slowing down?

Answer 20

It is decelerating

Question 21

Falling objects accelerate at (…)m /s²

Answer 21

10

Question 22

A typical acceleration for a car is (…)m/s²

Answer 22

5

Question 23

How can the acceleration be calculate from a velocity-time graph?

Answer 23

Calculating the gradient

Question 24

How can the distance travelled by an object (or displacement of an object) can be calculated from a velocity-time graph?

Answer 24

by calculating the area under the graph

may need to find area using triangles or trapezium area calculations

Question 25

What is uniform acceleration?

Answer 25

When the rate of change of velocity is constant

v² - u² = 2as

Question 26

Explain what happens when an object falls through a fluid

Answer 26

An object falling through a fluid initially accelerates due to the force of gravity.

Eventually the resultant force will be zero and the object will move at its terminal velocity (no resultant force, velocity constant so acceleration is zero)

Question 27

4 marker

Why does a car have a maximum speed?

Answer 27

there is a maximum forward force (provided by the motor)

as the speed of the car increases, air resistance increases

until air resistance is equal in size to forward force

so the car can no longer accelerate

Question 28

4 marker (indicative)

Describe what happens to the braking distance if speed doubles (refer to kinetic energy in the answer)

Answer 28

• doubling speed increase the kinetic energy
• kinetic energy increases by a factor of 4
• work done (by brakes) to stop the car increases
• work done increases by a factor of 4
• work done is force × distance and braking force is constant
• so if work done increases by 4 then the braking distance must increase by 4

Question 29

How would changing the shape of a car so that it is more streamlined affect its top speed?

Answer 29

decreases surface area

so less air resistance

so reaches a higher speed

Question 30

In circular motion, in which direction is the resultant force?

Answer 30

Towards the centre

Question 31

2 marks - key exam technique

As an object moves along a runway, its acceleration decreases even though the force/power remains constant, why is this?

Answer 31

As speed increases, air resistance increases

reducing the resultant force

Question 32

4 marks

Explain the changing motion of the skydiver in terms of the forces acting on the skydiver

Answer 32

initially air resistance is less than weight / gravity so the skydiver accelerates

acceleration causes the air resistance to increase

resultant force decreases to zero

so the skydiver falls at terminal velocity

Question 33

3 marks

Explain why a skydiver reaches a much higher speed when jumping from a higher height?

Answer 33

The higher the altitude the less dense the air

so air resistance on the skydiver was less

so skydiver was able to accelerate for a longer time before reaching terminal velocity