Name Coy Period: | Acceleration and Average Speed | Acceleration | Acceleration 1s how fast you change speed OR how much the speed changed in a certain amount of time. AV «— Change of Speed (in meters/sec) AT —#—— Change of Time (in seconds) Acceleration (in meter/sec?) Speed equal change of distance divided by change of time. АМ = V:- Y; АТ = T, - Ty Ch. 2:1 a = AS/AT, not a = S/T, Why? If a car is traveling at 60 m/s for 20 sec, 5 = 60 m/s, but AS = 0 m/s. No change of speed: no acceleration. — Example: Calculate Acceleration Step 1: Variables Ex. A plane starts at rest and ends up going 200 m/s in 10 secs. Calculate acceleration. Step 2: Find AS Step 3: Formula Step 4: Solve S, = 0 m/s (“starts ar rest”) a = (200 m/sy(10 s) = 20 m/s* S2 = 200 m/s А5 = $ - 5, a= AS/AT AT = 10 seconds = 200 - 0 = 200 m/s a=? Example: Ex. A race car starts at 400 m/s and Deceleration means an Calculate Deceleratior : then stops in 20 seconds. Calculate the car's acceleration. Step 1: Variables Step 2: Find AS Step 3: Formula object is slowing down and has a negative sign. Step 4: Solve a = (-400 m/s)/(20 s) = -20 m/s? S1= 400 m/s | S,= 0 m/s (“then stops”) 0 “don 2 mis a= AS/AT AT = 20 seconds Mn = 5 pr а=? NOTICE NEGATIVE AS Negative sign means deceleration. | | Average Speed | | Speed vs. Velocity & = Déotal Speed is a Scalar ave = a . Total Velocity isa Vector Ex. A 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 4 miles 2 hours oT 0 miles 1 hour - Careful—distance 15 O miles because “stops ... for lunch” 8 miles 3 hours | TOTALS: 12 miles | 6 hours | Save — Diotat Total = 12 mi/6 sec = 2 mph cstephenmurray.com 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—yector. | A boat is pulled by a 53 newton force—scalar. Vectors have magnitude and direction. Velocity is a vector with magnitude and direction. Copyright © 2004, C. Stephen Murray speed vs. time graphs; Ch. 2:1 E =H LH and dvectrom E Speed (S) ar Velocity (Y) Scalar (S) or Vector (V) Match the variables with quantities, Vv A bike goes 25 m/s toward \/ 40 mph toward Dallas. la=_ FM / $ & | 23 kilograms main street | — ил (5 | G A 25N force pulls on a 250rv=_23 mls 23 sec > A person walks 4 mph. Wagon. 3.т= _# 3 La 3 m/s? —$ A plane flies 200 m/s. \/__10 meters up the bill 4.D 3 dl 23 meters/sec . | | s.F=_23 M 23 meters М A bird flies 100 mph due S 12 meter per sec”. 6.T= 23 Sw 23 newtons south. o 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. Variables: Solve: L-2 Variables: Solve: 6 - 250 Vi = 2/6 K= — Vi= 2S0mp А = Из = г. / a | y == - 6 ws A Vi: O > 250 T= э се | #4 T=>25 Ses A = Ze Formula: Zz | Formula: | A EX | A-2m/ ja | A 710 0 TT T mPh/S SE A guy bikes 13 miles in 1 hour, then rests for an hour. A dragster's top acceleration is 60 m/s”. Ts 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: ol Variables: Solve: y, | | - == но d = о“ 5 = Om iz O m/< 2-— 2= 186 M/S + = Ч he | qi += 3 eC Formula: | 0 I Formula: S = a ‚ Р = A + +V, + Speed vs. Time Speed vs. Time Which graph segments ; fit the following: A Constant speed: A+C Deceleration: B Speed Accelerating: D Speed (m/s) 0 2 4°6 8 1 12 | lime The slope of a Speed vs. time graph means: Velo: Жи» Find the acceleration for the above graph: pU-O be | The siope of à Speed vs. time graph means: G2-S1 o. 7. | ©. k= + = 10 7 (07 b/s AtceleraHen estephenmurray.com Copyright O 2004, C. Stephen Murray Time (sec)
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