P8.1 - physics on the move

Question 1

How would you measure … the of a 100m sprinter?

• speed
• distance
• time

Answer 1

Speed - electronic timing system
Distance - measuring tape/trundle wheel
Time - pressure sensor to start? Laser beam to end

Question 2

How would you measure … the of a car on a road

• speed
• distance
• time

Answer 2

Speed - speed gun
Distance - measuring tape/trundle wheel
Time - time between two photos

Question 3

How would you measure … the of a cyclist?

• speed
• distance
• time

Answer 3

Speed - wheel sensor
Distance - wheel diameter
Time - magnetic sensor that detects one rotation (how quickly one rotation happened)

Question 4

Typical speed of a person walking (m/s), then convert it to mph

Answer 4

1 m/s, 2.2mph

Question 5

Typical speed of a person running (m/s), then convert it to mph

Answer 5

5m/s, 11mph

Question 6

Typical speed of a person cycling (m/s), then convert it to mph

Answer 6

7m/s, 15mph

Question 7

Typical speed of a person Olympic cycling (m/s), then convert it to mph

Answer 7

20m/s, 45mph

Question 8

Speed of Strong wing (m/s), then convert it to mph

Answer 8

13m/s, 30mph

Question 9

Average speed of car (m/s), then convert it to mph

Answer 9

22m/s, 50mph

Question 10

Typical speed of train (m/s), then convert it to mph

Answer 10

56m/s, 125mph

Question 11

What is reaction time? (And give an example of timing a runner)

Answer 11

The lag between you seeing something, and your action as a result

ie. when runner finishes finishing line light reflects from runner, hits your retina, impulse travels to brain, back down to finger, then presses stop button on stopwatch

Question 12

What is a human’s average reaction time?

Answer 12

0.2 seconds

Question 13

How do you measure reaction time + improve it?

Answer 13

Catch a falling ruler, play video games

Question 14

What is thinking distance? (In a car)

Answer 14

Distance that a car travels while the driver reacts to a hazard (so before they react, ie. pressing brakes)

Question 15

What factors affect thinking distance (and why)?

Answer 15

• alcohol consumption
• using drugs/ medicines
• being tired
  AFFECTS reaction time of individual
• distraction by other ppl in the car
• eating/drinking
• using radio/ Satnav
  AFFECTS as they are distracted, so not on full alert

Question 16

How would being under the influence of drugs/alcohol make you more likely to be in a car crash?

Answer 16

Since your reaction time greatly increases, perhaps double or triple that of it would normally be.

That means you could travel almost double or triple the distance before even braking

Question 17

What is braking distance?

Answer 17

The distance that a car travels while the driver is braking

ie. after the driver applied the brakes

Question 18

What factors affect braking distance? (4)

Answer 18

• quality of brakes (ie. are they worn out, can they apply pressure effectively)
• surface that the car is driving on (ie. if ice then less friction = larger braking distance)
• speed of the car while travelling
• mass of car/ passengers within
  larger mass = larger kinetic energy = more energy to be converted to stop = larger braking distance

Question 19

What is stopping distance?

Answer 19

The total distance that the car travels from the moment the driver sees the problem to until the car is stationary

Ie. Thinking distance + braking distance

Question 20

What is the thinking distance and braking distance for 50mph?

Answer 20

15m = thinking distance
36m = braking distance

Question 21

What is the thinking distance and braking distance for 30mph?

Answer 21

Thinking = 9m
Braking = 14m

Question 22

What is the thinking distance and braking distance for 70mph?

Answer 22

Thinking distance = 21m

Braking distance = 75m

Question 23

What is key about the relationship between speed and braking distance?

And what does that mean in terms of safety?

Answer 23

The higher the speed, the braking distance drastically increases (imagine the corona curve), so a much much larger distance is needed to stop a car travelling at 70mph (almost 100m)

Therefore, it’s very dangerous to travel at high speeds (could easily crash anywhere, and you have no control)

Question 24

explain the dangers of a large deceleration

Answer 24

• a large force is exerted on the passengers and the vehicle
• seatbelt can cause compression injuries
• injure internal organs (ribs stopped by seatbelt, but organs are still moving)

Question 25

what is the equation to find out the forces involved in typical situations on a public road?
(if you have mass + acceleration)

Answer 25

F = M x A

Question 26

suggest what causes a ‘large deceleration’ on the road

Answer 26

braking hard

Question 27

what in a car is designed to reduce the effects of the large deacceleration?

Answer 27

• seat belts
• crumple zones
• air bags

Question 28

how does a seat belt reduce the injury effects of the large acceleration?

Answer 28

• slightly stretches under large forces

- which increases the distance the passengers move (reducing force experienced)

Question 29

how does a crumple zone reduce the injury effects of the large acceleration?

Answer 29

• soft areas at front of car DEFORM (absorbs energy to compact)
• increases time taken for car to stop
  REDUCE FORCE/ACCELERATION

Question 30

how does an air bag reduce the injury effects of the large acceleration?

Answer 30

• prevents head from hitting steering wheel
• or jerking back (neck injuries)
• head hits bag = slows down = increase time = less force on neck