chapter 3 - motion

Question 1

displacement (s)

Answer 1

• distance moved by a body in a specified direction
• VECTOR (magnitude and direction)
• measured in metres

Question 2

speed (v)

Answer 2

• rate of change of distance
• SCALAR
• instantaneous speed is the speed at any given instant
• average speed = distance/time
  measured in m/s

Question 3

measuring speed

Answer 3

using one light gate
- timer starts when the card breaks the light beam
- stops when the other end passes through
- computer calculates speed by dividing card length by time taken
using a motion sensor
- motion sends out a series of ultrasonic pulses
- pulses reflect from nearby objects and return to a detector
- the software provides a very precise timer to measure the time elapsed between sending and detection of the pulse
using a video camera
- need a clear view of the distance scale
- the recording can be used to measure the time take

Question 4

velocity

Answer 4

• rate of change of displacement of a body
• velocity = change in displacement / time taken
  VECTOR
• constant velocity means it has equal changes in displacement in equal time intervals
• non-constant velocity means its accelerating
• measured in m/s

Question 5

acceleration

Answer 5

-rate of change of velocity of a body
- change in velocity(v-u) / time taken
- measured in m/s^2
- VECTOR
- a body accelerates if speed changes or direction changes
- constant acceleration means = velocity changes in = time intervals

Question 6

displacement time graph

Answer 6

• gradient = velocity
• horizontal = stationary
• positive gradient = constant velocity
• curved graph = acceleration/ decceleration

Question 7

velocity time graph

Answer 7

• gradient = acceleration
• horizontal = constant velocity
• curved = changing acceleration
• area under = displacement

Question 8

deriving suvat

Answer 8

• v= u +at - gradient of v/t graph
• s = 1/2(u+v)t - average v*time
• s = ut +1/2at^2 - sub v=u+at into s = (u+v )/2 t
• v^2 = u^2 +2as - sub t = (v-u)/a into v = u +at

Question 9

all suvat

Answer 9

v = u + at
s = ut +1/2at^2
s = 1/2(u+v)t
v^2 = u^2 + 2as

Question 10

g

Answer 10

acceleration due to gravity
g is + for falling objects
g I s- for upwards projection

Question 11

how galileos experiments overturned Aristotle ideas of motion

Answer 11

• show that constant force is not needed to maintain motion but force is needed to start/stop/chanhe speed and direction

Question 12

relationship between d and t for an object in freefall from rest

Answer 12

s is proportional to t^2

Question 13

effect of mass on the acceleration of an object in free fall

Answer 13

no effect

Question 14

projectiles suvat

Answer 14

• air resistance is negligable
• path is a parabola
• t1 = t2 (total t = 2*t1)
• Uh is constant bc aH is 0 (Uh= Vh)
  VERTICAL
• v = 0
• a = -9.81
  HORIZONTAL
• u = v
• v = u
• a = 0
  projectile = object acted upon only by gravity

Question 15

what angle results in max range (horizontal s)

Answer 15

45

Question 16

stopping distance

Answer 16

thinking + breaking
thinking - distance taken to put on the breaks (reaction time)
TD is prop to speed
TD = speed *reaction time
breaking - distance taken for car to stop
BD is prop to speed^2

Question 17

vector
scalar

Answer 17

size and direction
just size

Question 18

vector adding ( same line)

Answer 18

2 vectors in the same direction add to make one big vector

Question 19

vectors at right angles

Answer 19

use pythagorus to find the size and trig to find the angle

Question 20

scale drawing vectors

Answer 20

• chose a suitable scale
• draw a vector to represent one
• draw the next vector with its tail starting at the tip of the first one
• the resultant vector connects the start point to the very end
• can find length / angle with rule/ protractor

Question 21

finding horizontal / vertical from a resultant vector

Answer 21

x = F cos(θ)
y = F sin (θ)

Question 22

describe how you would experimentally find the speed of a ball

Question 23

how would you find acceleration of free fall (using galileos method and modern day equipment)

Answer 23

• set up two light gates - attached to a data logger
• roll a ball between them
• width of ball is known (d is known)
• t is recorded
• comp works out v and u using d/t and can find a using v-u/t