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Harris Academy S3 Physics > Motion & Forces > Flashcards

Motion & Forces Flashcards

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1
Q

Two identical cars are crash-tested. One is at 56mph, the other is 40mph.
Which car was crashed at 56mph? Explain your answer.

A

B was crashed at 56mph.

Crashes at higher speeds will do more damage.

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2
Q

This car is stationary. What are the forces acting on the car?

A

Weight and normal reaction force

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3
Q

What is the difference between average speed and instantaneous speed?

A

Average speed - measured over a distance or journey

Instantaneous speed - measured at one specific moment or point

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4
Q

Are these forces balanced or unbalanced? Explain your answer.

A

They are BALANCED - equal size, in opposite directions.

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5
Q

How can the force of friction be reduced?

A

Using oil / wax / ice / lubrication

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6
Q

What are the forces acting on the skydiver?

A

Weight (down)

Air resistance (up)

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7
Q

True or False: the elastic cable pulls down on the bungee jumper. This force is called tension.

A

FALSE.

The elastic cable pulls UP on the bungee jumper. This force is called tension.

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8
Q

A car travels 420 metres in a time of 17 seconds.
What is the average speed of the car?

A

d = v x t
420 = v x 17
v = 420 / 17
v = 24.7 ms-1

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9
Q

A cyclist is moving at 8 metres per second. How far will they travel in 5 minutes?

A

d = v x t
d = 8 x (5 x 60)
d = 2400 m

!!! convert minutes to seconds !!!

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10
Q

List three safety features of modern cars.

A

Seatbelts

Airbags

Crumple zone

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11
Q

What is the name of the force that affects an object moving at speed through the air?

A

Air resistance

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12
Q

What are the units for force?

A

N
(newtons)

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13
Q

Describe the motion of an object when the forces are balanced.

A

The object will
- stay at rest
or
- move at a constant speed in a straight line.

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14
Q

Are these forces balanced or unbalanced? Explain your answer.

A

They are UNBALANCED - there is 100 N in total, all towards the right.

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15
Q

What are the units for distance?

A

m
(metres)

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16
Q

When designing a car, how can the force of air resistance be reduced?

A

This is called streamlining.

  • lower to the ground
  • smooth shape
  • smaller surface area
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17
Q

Are these forces balanced or unbalanced? Explain your answer.

A

They are BALANCED - equal size, in opposite directions.

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18
Q

This car is moving forward at a constant speed. What are the forces acting on the car?

A

Weight (down), Normal reaction (up), thrust (forwards), air resistance (backwards), friction (backwards)

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19
Q

A car is travelling at a constant speed of 12 metres per second.
What distance will the car travel in 30 seconds?

A

d = v x t
d = 12 x 30
d = 360 m

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20
Q

Describe the motion of the object in this speed-time graph.

A

Constant positive acceleration

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21
Q

Re-word this statement to make it correct:
“When you cycle really fast on your bike, you often feel the wind pushing back against you.”

A

“When you cycle really fast on your bike, you often feel the air resistance pushing back against you.”

22
Q

What are the units for speed?

A

ms-1
(metres per second)

23
Q

What are the three quantities in this formula?

A

d - distance
v ‘bar’ - average speed
t - time

24
Q

What are the units for time?

A

s
(seconds)

25
Q

Describe the motion of this object.

A

The forces are BALANCED so the object will stay at rest OR continue at a constant speed in a straight line.

26
Q

For the object in this speed-time graph, what can be said about the forces acting on the object?

A

The forces are BALANCED because it is moving at a constant speed

27
Q

What are the units for acceleration?

A

ms-2
(metres per second squared)

28
Q

What equipment would you need to be able to determine the average speed of a cyclist?

A

Stopclock (timer)

Metre stick (measuring tape, trundle wheel)

29
Q

What is the name of the force from a vehicle’s engines that makes it accelerate?

A

Thrust

30
Q

Re-word this statement to make it correct:
“A seatbelt will make you speed up if you are in a car accident. It does this by applying a forwards force against your body.”

A

“A seatbelt will make you slow down if you are in a car accident. It does this by applying a backwards force against your body.”

31
Q

Describe the motion of the object in this speed-time graph.

A

Constant negative acceleration

32
Q

How does this cyclist reduce the force of air resistance acting against them?

A

- wearing skin-tight clothing

- crouching down and making their body as small as possible

- wearing an aerodynamic helmet

33
Q

What are the three quantities in this formula?

A

d - distance
v - (instantaneous) speed
t - time

34
Q

Describe the motion of this object.

Explain your answer.

A

The object will accelerate to the right.

There is an unbalanced force acting on it.

35
Q

Describe what would happen to an object if the forces on it are UNBALANCED.

A

The object would accelerate (in the direction of the unbalanced force)

36
Q

What is the name of the force caused by gravity pulling on an object?

A

Weight

37
Q

Describe the motion of an object when there is an unbalanced force acting on it.

A

The object will accelerate (in the direction of the unbalanced force).

38
Q

How would you do an experiment to determine the average speed of a person walking?

A

Use a metre stick to measure the distance
Use a stopclock to measure the time
Use the formula d = v x t to calculate the speed

39
Q

What is the name of the force that pushes UP on an object, when it is at rest on a solid surface?

A

Normal reaction force

40
Q

What is the definition of acceleration?

A

Acceleration is the change in speed per second.

41
Q

What are the forces acting on the rocket (just after take-off)?

A

Weight (down)

Thrust (up)

42
Q

What is the name of the force that exists when two solid surfaces are in contact?

A

Friction

43
Q

A rocket travels 10 km in a time of 38 seconds. What is its average speed?

A

d = v x t
10,000 = v x 38
v = 10,000 / 38
v = 263 ms-1

!!! convert km to metres !!!

44
Q

What are the forces acting on this person?

A

Weight (down)

Normal reaction force (up)

45
Q

For the object in this speed-time graph, what can be said about the forces acting on the object?

A

The forces are UNBALANCED because the object is accelerating

46
Q

How would you do an experiment to measure the instantaneous speed of a toy car?

A

Use a lightgate (and computer) to measure the time taken to pass through the lightgate (t)

Measure the length of the car (d)

Use the formula d = v x t to calculate the speed

47
Q

What is the name of the force that exists in a rope, string, cable, elastic band… ?

A

Tension

48
Q

True or false: an object can be at rest (stationary) even if forces are acting on it.

A

TRUE

If the forces on an object are BALANCED, it can stay at rest (or continue at a constant speed in a straight line)

49
Q

What are the four quantities in this formula?

A

a - acceleration

v - final speed

u - initial speed

t - time

50
Q

Describe the motion of the object in this speed-time graph.

A

Constant speed
(or steady speed)

Harris Academy S3 Physics (4 decks)

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