Unit 1 Notes Problems-Solved (p

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Practice Problem::

Practice Problem: What is the average of the following times? 3.54 seconds, 3.66 seconds, 3.45 seconds, 3.59 seconds How do you find the average of a group of numbers? Copy the question in the TOP box on page 44 and answer it… (3.54 + 3.66 + 3.45 + 3.59) 4 = 3.56 s To find an average you add each measurement and get the total, then you divide by the # of measurements taken.

Practice Problem—Copy this question in the BOTTOM box on page 44 and answer it…:

Practice Problem—Copy this question in the BOTTOM box on page 44 and answer it… What is the average speed for a marble that travels 3 meters in a time of 2.65 seconds? Speed = Total distance c hange in time s = d D t = 3 m 2.65 s = 1.13 m/s

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A person walks 10 meters to the right, then 5 meters to the left, then 8 meters to the right, then 14 meters to the left, then 26 meters to the right. What is the person’s distance? d = What is the person’s displacement? D x = Practice Problem—Copy this question in the TOP box on page 45 and answer it… + 10 - 5 + 8 - 14 + 26 = +25 m right 10m + 5m + 8m + 14m + 26m = 63 m Scaler quantity: Direction does not matter. (Add them all together). Vector quantity: Direction matters. (Going right is “+” and left is “-” ).

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A person moving at 4 m/s is slowing down at a rate of -1 m/s 2 . Draw the motion diagram for this negative acceleration. Practice Problem—Copy this question in the BOTTOM box on page 45 and answer it… 0 m 2 4 6 8 10 m 1 3 5 7 9 4 m/s 3 m/s 2 m/s 1 m/s

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A woman runs 400 meters (1 lap) around the track in a time of 55 seconds. What is her average speed? What is her average velocity? Practice Problem—Copy this question in the TOP box on page 46 and answer it… s = d D t = 400 m 55 s = 7.27 m/s velocity= displacement c hange in time (change in position) v = D t D x = 0 m 55 s = 0 m/s

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Sketch the graph below with the following three situations: Practice Problem—Copy this question in the BOTTOM box on page 46 and answer it… x(m) t(s) 1 3 2 Moving forward slowly at constant speed (start from 0 ) 2. Moving forward quickly at constant speed (start from 0 ) 3 . Moving backward slowly at constant speed (start from 0 )

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What is the acceleration of a car that goes from rest to 20 m/s in a time of 4 seconds? What is the acceleration if the same car if it goes from 35 m/s to a stop in a time of 7 s? ( ) Practice Problem—Copy this question in the TOP box on page 47 and answer it… a v i v f D t a v i v f t a = D t ( v f – v i ) = 4 s 0 m/s 20 m/s – = 5 m/s 2 ( ) a = 7 s 35 m/s 0 m/s – = -5 m/s 2

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Do the unit conversions below as a REVIEW: 100 km/ hr to _____ m/s 50 m/s to _____km/ hr Practice Problem—Copy this question in the BOTTOM box on page 47 and answer it… x = 27.8 m/s 100 km hr 1 km 1000 m x 3600 s 1 hr 1 km = 1000 m 1 hr = 3600 s Conversions : x = 180 km/ hr 5 0 m s 1 km 1000 m x 3600 s 1 hr

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Do the unit conversions below as a REVIEW: 45 m/s to _____km/ hr Convert your answer from km/ hr to miles/ hr Practice Problem—Copy this question in the TOP box on page 48 and answer it… x = 162 km/ hr 45 m s 1000 m 1 km x 1 hr 3600 s 1 km = 1000 m 1 hr = 3600 s Conversions : x = 101 mph 162 km hr 1 km = 0.6214 mile Conversions : 0.6214 mi. 1 km

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Usain Bolt has a maximum speed of about 13 m/s. How fast is this in miles per hour? 13 m/s to _____mi/ hr Practice Problem—Copy this question in the BOTTOM box on page 48 and answer it… x = 29 mph 13 m s 1609 m 1 mi x 1 hr 3600 s 1 mile = 1609 m 1 hr = 3600 s Conversions : 