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🌌 > P8.1 > Flashcards

P8.1 Flashcards

1
Q

How would you measure the speed or a 100m sprinter?

A
  • method = electronic time
  • distance = tape measure
  • time = pressure sensor to st art and laser broken to end
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2
Q

How would you measure the speed or a car on a road?

A
  • method = speed camera/speed gun
  • distance = trundle wheel to make road or d = s x time taken for reflection/ 2
  • time = time between 2 photos or pulses
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3
Q

How would you measure the speed of a cyclist?

A
  • method = wheel sensor
  • distance = diameter of wheel
  • time = magnetic sensor to detect rotation
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4
Q

How would you measure the speed of any moving object?

A
  • method = Satnav
  • distance = comparison of 3 satellites to distance
  • time = electronic timer
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5
Q

How do you convert from mph to km/hr?

- convert 30mph to km/hr

A
  • 1.6km per mile
  • x by 1.6
  • 48km/hr
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6
Q

How do you convert from km/hr to m/s?

- convert 48km/hr into m/s

A
  • divide by 3600 to turn hour into seconds and then x 1000 to change from km to m
  • so just divide by 3.6
  • 13.3 ≈ 13m/s
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7
Q

How do you calculate acceleration?

A

Change in velocity / time

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8
Q

What is a typical speed for walking?

A
  • 1.5 m/s (5.4km/hr or 3.4mph)
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9
Q

What is a typical speed for running?

A
  • 5 m/s (18km/hr or 11mph)
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10
Q

What is a typical speed for cycling?

A
  • 7 m/s (25km/hr or 15mph)
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11
Q

What is a typical speed for cars in a build-up area and a motorway?

A
  • build up areas = 13m/s (47km/hr or 30mph)
  • motorway = 31m/s (112km/hr or 70mph)
  • average = 22m/s (79km/hr or 50mph)
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12
Q

What is a typical speed for a train?

A
  • up to 55m/s (88km/ hr or 92mph)
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13
Q

What is a typical speed for a breeze?

A
  • 5m/s (18km/hr or 11mph)
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14
Q

What is a typical speed for a gale?

A
  • 20m/s (72km/ hr or 45mph)
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15
Q

What is a typical speed for the speed of sound?

A
  • in air = 340m/s (1224km/hr or 765mph)

- 330 - 340m/s

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16
Q

What’s the difference between the terminology of precise and accurate?

A
  • precise = small range when repeated

- accurate = close to the true value

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17
Q

What is the reaction time?

A
  • time taken from seeing something to the reaction (brake/pressing stopwatch button)
  • human reaction time = 0.2 secs
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18
Q

How can we measure human reaction time?

A
  • hold ruler between thumb and forefinger and forefinger should line up with 0 (3rd person at eye level may check if it’s lined up)
  • suddenly drop ruler and close thumb and finger when you catch it
  • measurement on ruler at point it was caught is how far ruler dropped in time it took you to react = longer distance = longer reaction time
  • use equation v2 - u2 = 2ad where u is 0, a is 10m/s and d is where you caught it and use a = change in v / time and rearrange to time = change in v / acc where ‘answer to earlier calculation’ is v and Acc = 10m/s
  • do lots of repeats and find mean distance, fair test (people, ruler)
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19
Q

What is the thinking distance?

A
  • distance traveled in the time it takes from seeing a potential problem and to start to apply the brakes
  • can be effected by the reaction time and the speed
  • speed increases = thinking distance increases at same rate as the drivers reaction time will stay constant but if higher speed = further you go in that time (can be effected my tiredness) as d=st
20
Q

What can affect thinking distance?

A
  • drinking alcohol/using drugs
  • being tired
  • distractions such as eating/drinking
  • using a satnav/ radio can mean increased speed
    (More distracted/ speed = distance the car travels is longer)
21
Q

Estimate the thinking distance for a car travelling at 50mph

A
  • 50mph in m/s is 22.2 m/s (x1.6 and /3.6)

- thinking distance = speed x reaction time (0.2 seconds) = 4.5m (2s.f)

22
Q

Calculate the reaction time for a student who gets 25cm using the ruler drop

A
  • square root of 2 x 10 x 0.25 (convert to m) = 2.23 m/s

- speed = d/t so 0.25/2.23m/s = 0.1118s or 0.11 s to 2 s.f.

23
Q

What is the braking distance?

A
  • distance taken to stop once the brakes have been applied
  • braking distance and speed = squared relationship = if speed doubles then braking distance increases 4- fold (2 squared) and trebles then increases x3 (a little less)
24
Q

What can affect the braking distance?

A
  • speed = faster you’re going, the further it takes to stop
  • mass = more mass so stops slower
  • condition of the brakes = worn/faulty can’t brake with as much force
  • grip of the tires = more likely so skid when road is dirty, ice or wet or if they’re bald (tires = min. tread depth of 1.6mm)
  • ice or leaves on road could reduce grip
25
Q

What is the stopping distance?

A
  • total distance travelled from moment deliver sees a problem to coming to a stop
  • thinking + stopping distance
26
Q

What affects the stopping distance?

A
  • drivers need to leave space in front so they can stop safely which is at least equal to stopping distance to their speed
  • speed limits = important = increases then thinking distance increases
  • braking distance and speed = squared relationship
27
Q

How do brakes stop a car?

A
  • the brakes of a car do work on the cars wheels
  • this transfers energy from cars ke store to thermal energy store of the brakes
  • stop a car = brakes must transfer all of this energy
  • doubling the mass doubles braking distance
28
Q

How can we calculate the braking force or braking distance?

A

Energy in cars ke store = work done by the brakes

- 0.5 x m (mass) x velocity squared = f (braking force)x d (braking distance)

29
Q

What’s the relationship between the thinking and braking distance?

A
  • energy 10mph increase in thinking distance, the braking distance increase by 3m
  • linear relationship
30
Q

How much does a car, single decker bus and loaded lorry normally weigh?

A
  • car = 1000kg
  • single decker bus = 10,000 kg
  • loaded lorry = 30,000 kg
31
Q

How does the deceleration change when the speed with a high speed compared to a driver with a low speed?

A
  • the lower speed driver = smaller thinking and braking distance and same reaction time
  • higher speed driver = higher thinking and driving distance and same reaction time
  • the gradient p/ deceleration is the same as the maximum force applied on the brakes hasn’t changed
32
Q

How can we interpret velocity time graphs for braking/thinking distances when an object decelerates?

A
  • stationary velocity = brakes applies as reaction time = area underneath gives thinking distance
  • deceleration = area underneath gives braking distance
  • gradient is same as force applied by brakes is same
33
Q

What is a collision?

A
  • a large negative acceleration or large deceleration
34
Q

How do seal belts allow you to come to a slower stop?

A
  • when a car stops you continue to move forward and the seatbelt stretched to bring you to a slower stop
  • if you don’t wear one then you accelerate at the original speed of the car
  • need to be replaced after a crash
35
Q

What happens if the deceleration is large?

A
  • compression injuries can occur from the seatbelt or internal organs can be damaged as they collide with the ribs
  • as a large deceleration needs a large force as f=ma
36
Q

How can a force on an object be lowered?

A
  • lowered by slowing the object down over a longer time such as decreasing deceleration as a= change in speed /time and f =ma
  • the longer it takes for a change in momentum, the smaller the force acting
37
Q

What affects the force you experience from a collision?

A
  • faster you go = greater force experienced in crash and more injuries
  • depends on the time taken for the collision to come to a stop
38
Q

How can we reduce the force using features?

A
  • crumple zones (diff density material so squish and longer stop and less force on people)
  • air bags = inflate so head hits something that allows you to deflate it slightly = slower stop and less forces acting on you
41
Q

How do bike helmets and shin pads reduce injury?

A
  • helmets = crushable layer of foam = increases time taken for your head to stop = reducing deceleration and forces acting
  • shin pads = pad deforms of something hits it= reduce deceleration and force on leg
42
Q

What is the g-force?

A
  • acc that you experience is about twice the acc due to gravity (9.81m/s^2) so you feel a force equal to times ‘X’ of your weight
  • 2g = 2 times weight
  • 3g = force is 3 times weight
43
Q

What do safety features in cars do?

A
  • increase collision times which reduce deceleration and forces = reduce injury
  • seat belts stretch slightly and air bags slow you down gradually
  • some also work by stopping you hitting heard surfaces like the dashboard or the road
44
Q

What are crumple zones?

A
  • areas at the front and back of a car which crumple up easily on a collision, increasing the time taken to stop
45
Q

What is the typical reaction time for a person?

A
  • 0.5 seconds or 500 milliseconds
  • 1 s = 1000 milliseconds
  • so 0.1 second = 100 milliseconds
46
Q

What happens to the thinking and braking distance when a car doubles in speed?

A
  • thinking distance = doubles

- braking distance = quadruples as it’s proportional to speed squared today

47
Q

What happens to your reaction time when it’s night and you’re tired?

A
  • increases
48
Q

Why do we repeat an experiment 3 times and take the average?

A
  • reduces the effect of random error
49
Q

How can you calculate deceleration knowing the force, speed, reaction time, distance and mass?

A
  • force is mass x acceleration

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