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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