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PAPER 2 : PHYSICS > P5 (part 3) > Flashcards

P5 (part 3) Flashcards

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1
Q

What is Newton’s First Law?

A

if the resultant force acting on an object is zero ( or if there’s no resultant force) and:

  • the object is stationary, the object remains stationary
  • the object is moving, the object continues to move at the same speed and in the same direction. so the object continues to move at the same velocity
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2
Q

What does the force “T” represent?

A

tension

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3
Q

Explain why an object being swung in a circle at a constant speed , does not have a constant velocity

A

although the object’s speed is constant, the direction is always changing , which means the velocity is always changing

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4
Q

What is inertia?

A

the tendency of an object at rest to stay at rest or moving object to continue moving

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5
Q

Give an example of a situation where an object has a large inertia

A

rugby player with the ball has a lot of mass (plus his team mate adding mass to him). He has alot of inertia

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6
Q

What is Newton’s Second Law?

A

the acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object

OR YOU CAN SAY:

If the force on an object is doubled, the acceleration will also double. but if the mass of an object is doubled, the acceleration will halve

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7
Q

What would the equation be for force?

A

force (N) = mass (kg) x acceleration (m/s2)

f = m x a

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8
Q

What is the definition of inertial mass?

A

is the ratio of force over acceleration

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9
Q

What symbol do we use to mean ‘approximate’?

A

≈

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10
Q

What is the typical approximate values of speed, acceleration and force of a person?

A

speed is ≈ 1.5 m/s

acceleration is ≈ 1.5 m/s2

force is ≈ 70 N

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11
Q

What is the typical approximate values of speed, acceleration and force of a car?

A

speed is ≈ 30 m/s

acceleration is ≈ 2 m/s2

force is ≈ 3000 N

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12
Q

What is the typical approximate values of speed, acceleration and force of an aeroplane?

A

speed is ≈ 300 m/s

acceleration is ≈ 3 m/s2

force is ≈ 600,000 N

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13
Q

What is Newton’s Third Law?

A

whenever two objects interact the forces they exert on each other are equal and opposite

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14
Q

Use Newton’s 3rd Law to explain how a fish can swim

A
  • as the fish moves its tail through the water, it exerts a force on the water
  • the water exerts a force back onto the fish, which is equal in size but opposite in direction
  • this pushes the fish forwards through the water
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15
Q

What two things must the driver of the car do in order to stop before hitting an obstacle?

A
  • see the obstacle and react

- then press the brake pedal and wait

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16
Q

What might affect the driver’s ability to do these things?

A
  • Worn brakes
  • road conditions
  • poor weather
  • drugs
  • alcohol
  • distractions
  • the speed they are going
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17
Q

What is meant by the term ‘reaction time’

A

The time it takes for a person to react to a stimulus. (NOT the speed at which they react)

the typical range of human reaction time is : 0.2 - 0.9secs

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18
Q

Write a method for an experiment to investigate reaction time

A

step 1: person A should sit with their arm resting on the edge of a table

step 2: person A holds out their hand with a gap between thumb & first finger. also person B holds the ruler ,vertically, with the zero at the top of person A’s thumb

step 3: person B drops it without warning & person A must catch it as fast as possible. then number level at the top of person A’s thumb is recorded in a table

step 4: repeat test serval times the calculates the mean distance that the ruler fell

19
Q

What is meant by ‘thinking distance’?

A

the distance the vehicle travels during the driver’s reaction time

20
Q

Why is there no change in speed during the thinking distance?

A

the driver hasn’t reacted yet and pressed the brake, so the speed will not change

21
Q

What is meant by ‘braking distance’?

A

the distance the vehicle travels while the braking force is being applied

22
Q

What happens to the speed of the vehicle during the braking distance?

A

the speed will decrease, until the vehicle stops

23
Q

What is meant by ‘stopping distance’?

A

the distance the vehicle travels during both the thinking and braking time. It is the sum of the thinking and braking distance

24
Q

What is the stopping distance with a car at 30mph?

A

23 meters

25
Q

What is the stopping distance with a car at 60mph?

A

73 meters

26
Q

What is the stopping distance with a car at 70mph?

A

96 meters

27
Q

List the factors affecting thinking distance

A
  • tiredness
  • drugs and alcohol
  • distractions
  • speed
28
Q

List the factors affecting braking distance

A
  • poor road conditions ( eg: loose surface)
  • bad weather - wet or icy conditions
  • poor condition of the vehicle - worn brakes or tyres
  • speed
29
Q

How do brakes work?

A

when you press the brake pedal, it causes the brake pads to clamp onto the brake disc. The friction is what causes the car to stop

30
Q

We say ‘work is done’ on the brakes. What do we mean?

A

‘work done’ means ‘energy transferred’. When the brakes are pressed, the friction force means energy is transferred between stores

31
Q

Describe the changes in the energy stores of the car and the brakes

A

energy is transferred from the kinetic store of the car to the thermal store of the brakes. This means the temperature of the brakes increases

32
Q

Why do the brakes get hotter if the vehicle is moving faster?

A

more force is needed to stop the car over the same distance so more energy is transferred. This raises the temperature of the brakes compared to slower speeds

33
Q

Why are very large decelerations dangerous?

A

large decelerations may lead to brakes overheating and loss of control

34
Q

How can you estimate a forces during a deceleration? What equations might you use? What will you need to estimate?

A

we can use Newton’s 2nd Law (F = ma) to estimate forces (this means we will firstly need to estimate mass)

then we need to estimate acceleration:

  • if we know final speed, initial speed and time, use:
    a = △v ÷ t
  • if we know final speed, initial speed and distance, use: a = v2-u2 ÷ 2s
35
Q

What is momentum?

A

is a measurement of mass in motion: how much mass is in how much motion

36
Q

What is the momentum of an object which is not moving?

A

zero

37
Q

What is the equation used to calculate momentum?

A

momentum (kgm/s) = mass (kg) x velocity (m/s)

p = m x v

38
Q

What is meant by ‘conservation of momentum’?

A

momentum before a collision is the same as momentum after a collision

39
Q

What can we say about the total momentum before and after the collision?

A

it is the same

40
Q

Harder Momentum Examples

A

A bullet with a mass of 0.03 kg leaves a gun at 1000 m/s. If the gun’s mass is 1.5 kg, what is the velocity of the recoil on the gun?

41
Q

Harder Momentum Examples

A

An ice skater of mass 67 kg is moving to the east at 4 m/s. She collides with a stationary man of 70 kg and she grabs hold of him to make sure he doesn’t fall over. What is their final velocity in this inelastic collision, and in what direction do they travel after the collision? Give your answer to 3 s.f

42
Q

Answers the first example

A

before: gun (p= 0kgm/s)
after: gun (m= 1.5kg and v = ?)
bullet (m= 0.03kg and v= 1000m/s)

mg(mass of gun)
vg (velocity of gun)
mb( mass of bullet)
vb( velocity of gun)

mgvg + mbvb = 0

1.5vg + 0.03 x 1000 = 0
1.5vg + 30 = 0
1.5vg = -30
vg = -30/ 1.5

vg = -20m/s

43
Q

Answers the second example

A

before: ice skater(m =67kg and v = 4m/s)
man(m= 70kg and v= 0m/s)

after: ice skater(m =137kg and v = ?)

momentum before: 268 + 0= 268kgm/s

because of the conservation of momentum, momentum after the collision is also 268kgm/s

137v = 268
v = 1.956...

v = 1.96m.s

PAPER 2 : PHYSICS (11 decks)

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