P2: Forces

Question 1

Vector vs scalar

Answer 1

• vector = magnitude + direction
• scalar = magnitude

Question 2

speed of walking

Answer 2

1.5 m/s

Question 3

speed of running

Answer 3

3 m/s

Question 4

speed of cycling

Answer 4

6m/s

Question 5

speed of sound

Answer 5

330 m/s

Question 6

what is acceleration

Answer 6

• rate at which velocity changes
• change in velocity/time
• m/s/s

Question 7

how can something have a constant speed but changing velocity

Answer 7

• velocity is a vector
• circular path = always changing direction
  • so velocity always changing
• also accelerating as
  • a = change in velocity/time

Question 8

distance time graph

Answer 8

• straight line = constant speed
• gradient = speed
  • if increasing = accelerating
  • if decreasing = declerating

Question 9

velocity time graph

Answer 9

• straight sloping = constant acceleration
  • steeper = larger acceleration
• horizontal line = constant velocity
• gradient = acceleration
• distance = area underneath

Question 10

Newtons first law

Answer 10

if there is no resultant force an objects motion will remain constant

Question 11

Newtons 2 law

Answer 11

• acceleration is directly proportional to the resulatant force
• inversley proptional to the mass
• f=ma

Question 12

what is inertia

Answer 12

• (an object tendency to remain in motion )
• how hard it is to change an objects velocity

Question 13

stopping distance

Answer 13

• stopping = thinking + braking
• thinking is distance travelled when reacting to hazard
• stopping distance is distance travelled whilst break is pressed

Question 14

how does speed effect braking distance

Answer 14

• To break work must be done
• kinetic energy = 1/2 x mass x velocity^2
• if the speed double the kinetic energy x4
• work done to stop the car needs to be x4
  • W=FxD
  • distance x4

Question 15

why can skidding happen

Answer 15

• brakes do mechanical work by apply force
• to transfer energy kinetic –> thermal
• if transfer happens to fast, brakes over heat and fail

= skid

Question 16

what is momentum

Answer 16

• tendency for an object to remain in motion

Question 17

why are airbags, seatbelts and crumplzones used

Answer 17

• increase the impact time
• reduces the rate of change of momentum
• reduces the impact/force

force =change in momentum/time

Question 18

newtons 3 law

Answer 18

every action has an equal and opposite reaction

Question 19

what is weigt

Answer 19

• force of attraction
• experienced as your are in Earth gravitational field

Question 20

centre of mass

Answer 20

from where the weight of an object acts from

Question 21

why does the moon orbit the earh

Answer 21

• resultant force acting on the moon towadrs centre of earth
• due to the earth gravitational field
• as the force is at a right angles to direction of travel
• it causes circular motion

Question 22

moment

Answer 22

turning effect of a force

Question 23

what is the principal of moments

Answer 23

• if an object is in equilibrium
• sum of all clockwise moments = sum of all anticlockwise moment

Question 24

what is gear

Answer 24

• device that transmits rotational effect
• from one place to another

Question 25

how do gear work

Answer 25

- Cog A has moment - Transferred to Cog B at point of contact - Cog B has different size and different perpendicular distance - = different sized moment - in the opposite direction