Chapter 9: Physics; Motion and Energy

Question 1

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Distance

Answer 1

• Represented as d
• Total scalar length an object travels
• Distance does not depend on direction

Question 2

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Displacement

Answer 2

• Represented as ∆d
• Vector that points from an object’s starting position to its final position
• Displacement depends on direction
• Displacement = final position - initial position
• ∆d = dfinal - dinitial
• Defined using: + or -, NSEW, Angles

Question 3

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Scalar

Answer 3

• Distance is a scalar quantity, meaning it depends on only magnitude and not direction.

Question 4

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Vector

Answer 4

• Displacement is a vector quantity as it depends on both magnitude and direction

Question 5

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Speed

Answer 5

• Represented by s
• Scalar Quantity that refers to the rate at which an object is moving
• Speed = distance/time
• E.g car travels 20 m/s (magnitude)

Question 6

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Velocity

Answer 6

• Represented by v
• Vector quantity that refers to the rate at which an object changes its position
• Velocity = displacement/time
• Has both magnitude and direction
• E.g car travels 20 m/s east (magnitude and direction)

Question 7

Velocity Formula

Answer 7

Question 8

Speed, Distance, Time

Answer 8

speed = distance/time
time = distance/speed
distance = speed x time

Question 9

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Acceleration

Answer 9

• Represented by a
• Vector quantity, rate of change of the velocity
• To accelerate, change your speed or your direction-or change both
• avg acceleration = (final speed - initial speed)/time or change in velocity/time
• can be written as a = v - u/t
• SI units are m/s/s or ms-2 or m/s2

Question 10

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How to calculate final speed

Answer 10

• Use formula for acceleration
• Where a = acceleration, v = final speed, u = initial speed, t = time taken
• final speed = initial speed + (average acceleration x time taken)
• v = u + at

Question 11

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Negative Acceleration

Answer 11

• When the object is moving in the positive direction, but the rate of change of velocity is negative, where a = v-u(neg)/time
• Negative value means that initial speed is greater than final speed, object is decelerating

Question 12

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Types of Acceleration

Answer 12

An object can be accelerating when it is:
* Speeding up: car speeds up
* Slowing down: car slows down
* Changing direction: car turns, changes velocity (can be at constant speed)

Question 13

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Acceleration due to gravity

Answer 13

• Falling objects accelerate towards the earth due to gravity
• Gravity = 9.8m/s, therefore acceleration due to gravity = 9.8 m/s/s or m/s2 (g-force)
• Falling objects do not reach enormous speeds due to friction and air resistance

Question 14

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Terminal Velocity

Answer 14

• When an object falls towards earth, it will eventually reach a point where the downwards force due to gravity is balanced with the upwards force of friction and air resistance. While the object still falls extremely fast, it will not speed up.
• Terminal velocity is the constant speed with which an object falls when air resistance balances the force of gravity.

Question 15

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Human tolerance and G-Force

Answer 15

• Human tolerance depends on the direction and the part of the body the force acts on
• Humans are more suited to tolerate horizontal forces as a vertical drop for long durations can disrupt blood flow to the brain

Question 16

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Newton’s First Law

Answer 16

An object at rest will remain at rest and an object in motion stays in motion with the same speed and in the same direction unless it is acted upon by an unbalanced force.

Question 17

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Inertia

Answer 17

It is the tendency of an object to resist any change to its motion or state, including changes to speed and direction

Question 18

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Unbalanced Force

Answer 18

• Unbalanced forces cause change in an object’s motion; a stationary object will accelerate, a moving object will change direction or speed
• For example, a book on a table is pushed to the right, friction acts to the left to slow the book down. The unbalanced force changes its state of motion and the book accelerates to the right.

Question 19

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Examples of Newtons First Law

Answer 19

• A driver of a car brakes suddenly, by intertia, the car and passenger lurches forward
• A runner continues to run past the finish line due to inertia
• A rolling ball on rough ground stops before a rolling ball on smooth ground because the rough surface offers more friction to act upon the moving object

Question 20

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Newton’s Second Law

Answer 20

• An object will accelerate in the direction of an unbalanced force acting upon it. The size of acceleration depends upon the mass of the object and the size of the force acting.
• If you push something, it moves in that direction
• If you continue to push, it will accelerate
• The heavier the object, the more force required
• The heavier the object, the less it will accelerate

Question 21

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Force, mass, acceleration (Newton’s Second Law)

Answer 21

Net Force (Newtons) = mass (kg) x acceleration (m/s/s)
m = fnet/a
a = fnet/m

Question 22

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Newton’s Third law

Answer 22

For every action force on an object, there is an equal and opposite reaction force back on the other object.

Question 23

Examples of Newton’s Third Law

Answer 23

• A nail is hit by a hammer = The nail exerts an equal force back on the hammer
• A book rests on a table and exerts its weight force onto the table = The table exerts an equal support force upwards on the book
• You stand a skateboard and push against a wall = The wall pushes back on you with equal force and you move away
• Rocket pushes gas out = Gas pushes rocket upwards

Question 24

How to convert between m/s and km/h

Answer 24

m/s x 3.6 = km/h
km/h ÷ 3.6 = m/s

Question 25

In terms of motion, when a cheetah is sitting stationary in the forest it has something in common with when it’s running on a straight course at 100km/hr. Explain

Answer 25

No acceleration = 0km/h/h

Question 26

How to solve for time with acceleration formula

Answer 26

time = final speed - initial speed over acceleration
t = (v - u)/a

Question 27

How to solve for intial speed

Answer 27

initial speed = final speed - acceleration x time
u = v - at

Question 28

Distance-Time Graph

Answer 28

• Shows how far an object travels over time
• Slope/gradient is equivalent to the object’s speed over a time interval
• The steeper the gradient, the faster the object is moving
• Speed = rise/run

Question 29

Speed-Time Graph

Answer 29

• Shows how an objects speed changes over time
• Flat line = constant acceleration
• Increase = increasing speed
• Decrease = decreasing speed
• Acceleration = rise/run
• Area under line gives distance travelled up to that point

Question 30

Velocity-Time Graphs

Answer 30

Question 31

Analysing Distance Time Graphs

Answer 31

Question 32

Converting km m etc.

Answer 32

Question 33

Converting Time

Answer 33