P3

Question 1

How do speed cameras work?

Answer 1

Usually, two photos of a vehicle are taken, the speed of the car is the distance travelled between the two pictures divided by the time taken between the pictures

Question 2

What unit is acceleration measured in?

Answer 2

m/s squared

Question 3

How do you work out acceleration?

Answer 3

Change in speed
————————
Time taken

Or force divided by mass (triangle)

Question 4

What is non-uniform motion?

Answer 4

When the acceleration of something changes gradually so it looks like a curve on a graph rather than straight lines

Question 5

What is work?

Answer 5

It is the energy transferred by something, measured in joules

Question 6

What is power?

Answer 6

How quickly work is done, measured in watts

Question 7

How are forces related to acceleration?

Answer 7

Forces cause objects to accelerate or decelerate, the greater the force, the greater the acceleration, the bigger the mass, the less acceleration.

          Force  ——————————
   Mass  |  Acceleration

Question 8

How and why is braking distance increased?

Answer 8

Bigger mass due to more kinetic energy
Friction between the tires and road is decreased
If braking force is decreased (i.e. worn brake pads)
If the vehicle is traveling faster (greater kinetic energy)

Question 9

How does thinking distance increase?

Answer 9

If the vehicle is travelling faster, if the driver is ill, tired or under the influence of drugs or alcohol, if the driver isn’t concentrating

Question 10

What is the relationship between speed/braking distance/thinking distance?

Answer 10

Thinking distance has a linear increase: double speed=double distance
Braking distance has a squared increase: double speed=quadruple distance, triple speed=braking distance x9 so the speed is squared

Question 11

What road safety regulations are in place to decrease thinking distance?

Answer 11

Because speed is such an important factor, regulations are in place to obey speed limits, keep your distance from the car in front and allow extra room/drive slower in bad weather conditions

Question 12

What increases fuel economy?

Answer 12

Less fuel consumption

Question 13

What are the advantages and disadvantages of electric cars?

Answer 13

A: No pollution when in use, cheaper fuel, cost effective, low maintenance
D: Few charging points, electricity comes from power station from fossil fuels, pollution during manufacturing, have to be refuelled often, takes a long time to charge up, silent cars are dangerous for pedestrians

Question 14

What are the alternatives to fossil fuel powered cars like diesel/petrol/electric?

Answer 14

Biofuelled and solar powered vehicles

Reduce pollution at point of use although still pollution during manufacturing

Question 15

What does fuel consumption of a car depend on?

Answer 15

• Energy required to increase KE
• Energy required to work against friction
• Driving style, speed, road conditions, wind, mass

Question 16

Give some examples of car safety features

Answer 16

For protection:
Seat belts, air bags, crumple zones (increase crash time), collapsible steering column, safety cage
For prevention:
Traction control (prevents skidding whilst accelerating so you can drive away quicker), anti-lock braking systems (prevent tires from skidding by increasing the area on the road, increasing friction, reducing braking distance) and reducing distractions (electric windows, paddle shift controls)

Question 17

What happens to do with momentum and force in a crash?

Answer 17

Momentum decreases which increases force on the passengers. The quicker the change in the momentum, the greater the force.
Momentum = Mass x velocity
Force= change in momentum / time taken

Question 18

How can you reduce stopping forces felt in a collision?

Answer 18

Increasing collision time or distance - by increasing stopping time (I.e. by using a crumple zone) you decrease acceleration and therefore decrease force

Question 19

What happens to a sky diver’s speed?

Answer 19

Acceleration due to gravity, air resistance but weight (W)>R so acceleration continues, speed (S) increases so R increases, R then increases to equal W and terminal speed is reached
Then parachute opens, R>W, R decreases S, R decreases until R=W and terminal speed is reached

Question 20

What happens to forces when an object falls at terminal speed?

Answer 20

KE doesn’t change because speed isn’t changing, GPE decreases because it’s transferred into internal or thermal energy in surrounding air particles by friction.

Question 21

What is mass, what is weight and how are they linked?

Answer 21

Weight is due to the force of gravity on an object (Weight = mass x gravity)
Mass is the amount of matter something contains
Weight = mass x gravitational field strength (or acceleration of free fall)

Question 22

What does gravitational potential energy depend on?

Answer 22

Mass, gravitational field strength and vertical height

Question 23

How do rollercoaster work and what happens to the kinetic energy of the car if the mass or speed changes?

Answer 23

Start high up (GPE), drop = GPE –> KE, highest speed and maximum KE at lowest point, climbs = KE-> GPE

Mass x2 = kinetic energy x2
Speed x2 = kinetic energy x4