Acceleration and Average Speed

Name:
Ch 21
Period: | Acceleration and Average Speed
Acceleration | i
Change of Speed
Acceleration a AV 4— (in meters/sec) a= AS/AT nota = SL
Acceleration is how fast (in meter/sec”) AT Change of = Why? If a car is traveling at
you change speed OR (in seconds) 60 m/s for 20 sec,
how much the speed 1 = ; i:
ea a Speed equal change of distance 5 = 60 m/s, but as = 0 m/s.
e aa divided by change of time. No change of speed:
amount of time. A no acceleration.
AV = Vr- Vi AT=T,-T,
Example: Ex. A plane starts at rest and ends
Calculate Acceleration
Step 1: Variables Step 2: Find AS
Si = 0 m/s (“starts at rest”)
up going 200 m/s in 10 secs.
Calculate acceleration.
Step 3: Formula Step 4: Solve
S,= 200 m/s АЗ = 52 - 5, a = AS/AT a = (200 m/s)/(10 s)
AT = 10 seconds = 200 - 0 = 200 m/s = 20 m/s”
+=”
Ex. À race car starts at 400 m/s and Deceleration means an
Example:
Calculate Deceleration
Step 1: Variables
S, = 400 m/s
S2 = 0 m/s (“then stops”) AS = Sy - Si
AT = 20 seconds = 0 - 400 = -400 m/s
Step 2: Find AS
En NOTICE NEGATIVE AS
| Average Speed |
Ex. À person walks 4 miles in 2 hours, then stops for
an hour for lunch. After lunch they walk 8 miles in
3 hours. Calculate the person's average speed.
Distance Time
Careful--distance is
O miles because 4 miles 2 hours
stops" “On ec ah 0 miles | hour
8 miles 3 hours
| TOTALS: 12 miles 6 hours
Save = О са! Trotal
= 12 mi/6 sec
= 2 mph
cstephenmurrav.com
then stops in 20 seconds.
Calculate the car's acceleration.
object is slowing down and
has a negative sign.
Step 3: Formula Step 4: Solve
а = АЗ/АТ a = (-400 m/s)/(20 s)
= -20 m/s?
Negative ALL
sign means deceleration.
Speed vs. Velocity |
Speed is a Scalar
Velocity is a Vector
“Speed has no direction; Scalars have no direction.
Velocity has direction; Vectors have direction.
A person walks 4 m/s—speed (no direction).
A person walks 2 m/s north— velocity (direction is given).
A car drives 60 mph toward Dallas—velocity.
A car drives 30 mph—speed.
A 14 newton force pull 30° left of north—vector.
A boat is pulled by a 53 newton force—scalar.
Vectors have magnitude and direction.
Velocity is a vector with magnitude and direction.
Copyright O 2004, C. Stephen Murray
Key
Name:
Period:
speed vs. time graphs:
Ch. 2:1
Speed (S) or Velocity (V)
Scalar (S) or Vector (V)
Match the variables with quantities.
\_ A bike goes 25 m/s toward Y 40 mph toward Dallas. а = 3 mis” 23 kilograms - Meds s
main street.
EEE ь 2) = - AN EIT > 7 2 S E и и
S A 25 N force pulls on a 2. мае 23 melers| = ae
S° À person walks 4 mph. wagon. Nb. 4 = © к 3 m/s? = Acceld EE
р, (2 сле”.
. | 4.D= 43 meters 23 meters/sec — Snolad
S A plane flies 200 m/s. Y 10 meters up the hill. = 3 = > su © Spe ed
Sa = АЗ Neutons 23 meters - Di strunce
\_ A bird flies 100 mph due S 12 meter per sec”. Ото Эд бое 23 newtons - Forl-
south. | : x rT
A person starts running from 2 m/s to 6 m/s in 2 seconds. A plane stops from 250 mph in 25 seconds.
Calculate the person's acceleration. Calculate the planes acceleration.
el 5 :
Variables: Solve: O Nim [a Variables: Solve: NIET |
Ge 6 Y - Amls V 2 O i \ = U a 20mph
Vi - = гу | S A Sec iF dane <Q
Sa | AY JCC
Vo = Lm < ‚| í A vv 50 Ou y
i Pa se «= te E pm ;
НЕЕ a sec | = 85 sec n, -2SO man
Formula: Formula: \A= me
- (Vo = v;) ( 2 Е save a A > se y
[email protected]= Le k= Qmli$ EN 1 PAR
A guy bikes 15 miles in 1 hour, then rests for an hour. A dragster’s top acceleration is 60 m/s”.
“Then he bikes 25 in 2 hours. If it accelerates for 3 seconds from the
What was his average speed for the trip? starting line, how fast will it be going?
Variables: Solve: 40 << Variables: Solve:
e UNED O=(Om|s” | Vo =(LOm2x3)+ 0
D= 15 mile s +45 mues Ч hours + i
(= 3Sec
| Но V, = 180 m/s
Formula: | D le Formula: f
miles / hour 3
) (TA
ТЕ С ) \
Speed (m/s)
6 8
Time (sec)
Speed vs. Time
10 12
ERE
Find the A for the above graph:
[56-0
10
В: Vp Ne
Speed
Speed vs
A
. Time
C
Time
Which graph segments
fit the following:
Constant speed: A ye
Peceteration:
eat ve Accelea len
DIA
ccelerating: D
b
The slope of a speed vs. time graph means:
Acce Lera
(: > peed
(UY
The slope of a position vs. time graph means: D
Spee o fi chang
er T1 me
(OV)
\ OV ey
1S dr Una ro
cstephenmurrav.com Ne > © = S
= We Y, = Omls
0 bom]?
Copyright O 2004, C. Stephen Murray
nme
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