ch 2 - accelerated motion

Question 1

what is acceleration?

Answer 1

• the rate of change of velocity of an object
• accelerating object = object with increasing speed
• unit = m s-2
• vector quantity
• gradient of velocity-time graph (straight line = constant, chnaging slope = changing acceleration)

a = v-u / t

Question 2

velocity - time graph?

Answer 2

• gradient of velocity-time graph = acceleration (straight line = constant, changing slope = changing acceleration)
• area under graph = displacement

Question 3

how to measure acceleration in the lab?

Answer 3

1. LIGHT GATES
   - from computer records time and is given length of card’s 2 interrupt sections

u = l1 / t2 - t1
v = l2 / t4 - t3
a = v - u / t3 - t1 (only gives approx. a value)

2. TICKER TIMER
   - for equal time intervals, find length and thus velocity
   - plot graph using values
3. MOTION SENSOR
   - computer calculates
   - poor precision

Question 4

what is constant acceleration/uniform acceleration?

Answer 4

when the change in velocity of and object is the same in the same time period

Question 5

s is the symbol of?

Answer 5

displacement

Question 6

u is the symbol of?

Answer 6

initial velocity

Question 7

v is the symbol of?

Answer 7

final velocity

Question 8

a is the symbol of?

Answer 8

acceleration

Question 9

t is the symbol of?

Answer 9

time taken

Question 10

the four equations of motion can only be used for?

Answer 10

• straight line motion
• an object with constant acceleration

Question 11

how to derive equation 1 of the equations of motion?

Answer 11

a = (v - u) / t

v = u + at

Question 12

how to derive equation 2 of the equations of motion?

Answer 12

avg. velocity = (u+v) / 2

displacement = avg. velocity * time taken

s = (u+v) / 2 * t

Question 13

how to derive equation 3 of the equations of motion?

Answer 13

from: v = u + at, s = (u+v) / 2 * t

s= (u + u + at) / 2 * t

s = ut + 0.5at²

Question 14

how to derive equation 4 of the equations of motion?

Answer 14

from: v = u + at, s = (u+v) / 2 * t

s = (u+v) / 2 * (v-u) / a

2as = (v+u) (v-u)

v² = u² + 2as

Question 15

what are the equations of motion?

Answer 15

i. v = u + at
ii. s = (u+v) / 2 * t
iii. s = ut + 0.5at²
iv. v² = u² + 2as

Question 16

what non-uniform acceleration?

Answer 16

when the velocity of an object changes by different amounts of the same time period (has changing gradient)

Question 17

non uniform acceleration in a graph?

Answer 17

• mark point on graph, draw tangent, find gradient

Question 18

what is free fall?

Answer 18

when an object accelerated due to gravity in the absence of any ither forces such as air resistance

symbol = g
value = 9.81 m s-2

Question 19

what are the lab experiments to find g?

Answer 19

1. ELECTORNIC TIMER, STEEL BALL, ELECTROMAGNET
   - current is switched off
   - ball falls and timer is automatically recorded
   - measure height h
   - use s = ut + 0.5at²
   - take several reading and plot graph
   BUT
   - em retains magnetism and slows ball’s fall, so t is too big
   - error in measuring height
2. TICKER TIMER
   - weight falls and pulls tape throught timer
   - increasing gap between dots shows acceleration
   BUT
   - friction slows weight fall
3. LIGHT GATE
   - drop plate through light gate
   - computer figures out

Question 20

are the vertical and horizontal motion affected by each other?

Answer 20

no

Question 21

vertical motion affected by?

Answer 21

weight, vertical acceleration

Question 22

horizontal motion affected by?

Answer 22

velocity, NOT gravity

Question 23

what are components?

Answer 23

the effect of a vector along a particular direction

Question 24

for velocicty v and angle O to the x direction the components are?

Answer 24

x direction = v cos O
y direction = v sin O

Question 25

when there is no air resistance, horizontal what and vertical what is constant

Answer 25

horizontal = constant velocity
vertical = constant acceleration