Topic 2 - Motion And Forces Flashcards

1
Q

What is a scalar quantity?

A

A quantity that only has magnitude but no direction.

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2
Q

What is a vector quantity?

A

A quantity that has both a magnitude and an associated direction

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3
Q

Three examples of vector quantities

A

Velocity
Displacement
Force

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4
Q

Give examples of scalar quantities

A
Temperature 
Mass 
Time
Speed 
Distance 
Energy
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5
Q

What is velocity

A

The speed of an object in a specific direction.

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6
Q

Equation relating average speed, distance and time

A

Average speed = distance / time

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7
Q

On distance/time graph, what value does the gradient of the line represent?

A

The speed

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8
Q

On a displacement/time graph, what value does the gradient of the line represent?

A

The velocity

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9
Q

What must be done to calculate speed at a given time from a distance-time graph for an accelerating object?

A

Draw a tangent to the curve at the required time

Calculate the gradient of the tangent

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10
Q

Equation for the average acceleration of an object

A

Acceleration = (change in velocity)/(Time taken)

A = (v-u)/t

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11
Q

Equation final velocity with initial velocity, distance and acceleration

A

V^2 - U^2 = 2 x a x x

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12
Q

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

A

It is equal to the area under the graph

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13
Q

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

A

The acceleration

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14
Q

Typical value of the speed of sound

A

330m/s

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15
Q

Typical value for human walking speed

A

1.5m/s

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16
Q

What is a typical value human running speed?

A

3m/s

17
Q

What is a typical value for human cycling?

A

6m/s

18
Q

What is weight?

A

The force that acts on an object due to gravity and the objects mass.

19
Q

Weight unit

A

N (newton)

20
Q

Gfs unit

A

N/kg

21
Q

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

A

When the object is changing direction; for example, moving in a circle

22
Q

Why does an object travelling at a constant speed in a circle not have a constant velocity?

A

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 constant changing

23
Q

What is the resultant force that acts on an object moving in a circle called, and in which direction does it act?

A

It is called the centripetal force and acts towards the center of the circle

24
Q

What is inertial mass?

A

A measure how difficult it is to change a given object’s velocity
The ratio of force over acceleration

25
Q

State Newton’s third law

A

Whenever two objects interact, the forces that they exert on each other are always equal and opposite.

26
Q

Equation to calculate object s momentum

A
Momentum = mass x velocity 
P = m x v
27
Q

Unit used for momentum

A

Kgm/s

Kilogram meters per seconds

28
Q

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

A

The total momentum before and after are equal

29
Q

Equation linking change in momentum, force and time

A
Force  = change in momentum/time
(Mv-mu)/t = F
30
Q

How can you measure human reaction times?

A

Using the ruler drop test
Person A and B hold each end of a ruler with 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.

31
Q

Why is it impossible that the 0cm mark is at the bottom?

A

So you can obtain the distance directly without having to calculate it; otherwise a zero error would need to be accounted for.

32
Q

What is the stopping distance of a vehicle equal to?

A

The sum of thinking distance and braking distance

33
Q

For a given braking distance , if the vehicle’s speed is increased, what can be said about its stopping distance?

A

The stopping distance is increased with an increase in speed

34
Q

Typical range of values for human reaction time

A

0.2 - 0.9 seconds

35
Q

Give three factors which can affect a drivers reaction time

A

Tiredness
Drugs
Alcohol

36
Q

Give two factors which may affect braking distance

A

Adverse (wet/icy) road conditions

Poor tyre/brake conditions

37
Q

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

A

Work is done by 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

38
Q

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

A

The braking force must also be increased

39
Q

State two consequence of a vehicle undergoing very large decelerations

A

KE converted to heat is very high causing brakes to overheat

Loss of control of the vehicle