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Unit 3
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Acceleration from gravity is 9.8 meters/sec/sec (SI) or 32 feet/sec/sec (English) That means that the speed of a falling object increases by about 10 m/sec every second that it falls.
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So after 2 seconds, an object is traveling 20m/sec After 8 seconds it is traveling about 80 m/sec
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The distance an object falls can be determined by the formula Distance = ½ gravity (time) ² D= ½ g t² A rock falls for 4.5 seconds before it hits the ground, how far did it fall? D = ½ g t² Gravity is 9.8 m/sec/sec or round to 10 to make it easier.
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½ (10) (4.5) ² 5m/sec² x 20.25 sec² = 101.25 meters.
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Speed is a scalar – only needs strength. Velocity is a vector quantity - needs to show the direction 60 MPH South 400 rpm clockwise
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Linear - goes in a straight line: trains, cars, etc.
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Rotational - goes in a circle: drill, flywheel, etc.
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Average speed = total distance/total time Displacement timespeed
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You travel 780 miles in 12 hours. Find your average speed. Average speed = total distance/total time
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780 miles/12 hours = 65 miles/hr or 65 MPH P =per
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You travel 200 miles in 4 hours, and then 210 miles in 3 hours. What is your average speed for the entire trip? Total distance/total time
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410 miles/7 hours = 58.57 MPH
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Distance = the actual distance traveled Displacement = the distance on the shortest line between where you started and where you ended up.
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Four cities all lie along a straight line as shown in the diagram. A delivery driver departs from City B, drives to City D, and then drives to City A.
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1. What distance does the driver cover during the described trip? If it takes him one hour, what is his average speed?
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7 + 9 + 9 +7 +5 = 37 miles so 37 MPH
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2. What is the driver’s displacement at the end of the described trip? If it takes him 1 hour, what is his average velocity?
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5 miles 5 miles/hour (west or left)
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Acceleration = Final velocity (vf) – Initial velocity (vi)/time vf-vi/t or ∆v/t
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Tells how much faster you go every second. Units in m/sec sec m/sec/sec or m/sec ²
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You are jogging at 2m/sec. You start to run and reach 10m/sec in 4 seconds. What is your acceleration?
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vf – vi/t 10m/sec – 2m/sec divided by 4 sec = 2m/sec/sec or 2m/sec ²
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Production rate = number produced/time
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100 washers come off a conveyor belt in 10 minutes. Find the production rate.
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100 washers/10 minutes = 10 washers/min
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Angular speed (rotational). There are 6.28 radians in one revolution. Common units for angular speed are: rev/min (rpm) rad/sec
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A flywheel goes 180 revs in 10 minutes. Find angular speed in revs/min and rad/sec. To find rad/sec: first change minutes to seconds (divide by 60) then times by 6.28 to change rev to radians.
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180 rev/10 min = 18 rev/min (rpm) 18 rev/min divided by 60 sec = 0.3 rev/sec x 6.28 rad/rev. = 1.88 rad/sec.
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