Sections 42 and 43 Updates amp Reminders The date and time of the final Thursday December 11 from 10 am to 12 pm MLT 208 There is no lab this week Test 1 will take place on Thursday 918 ID: 382893
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Slide1
Rectilinear Motion ContinuedSlide2
Some Practical Problems
An industrial sewing machine can stitch cloth at a rate of 3.8cm/s. During an 8-hour continuous run, how many METERS of stitching can be accomplished?
The current men's world record for the 100-meter dash is 9.58s. Usain Bolt from Jamaica set the record on August 16, 2009 at the World Championships in Berlin, Germany. What was Bolt’s average speed over this interval?
A lightning flash occurs and thunder is heard 2.4s later. How far away was the lightning bolt at its nearest point? Assume that the speed of sound is 343m/s. Be aware that the speed of light is so high that it can travel around Earth 7.5 times in one second.
In the above question, if the thunder
continues
to rumble for another 3.9s
after the start
, what was the most distant part of the lightning bolt?
A surface ship is bouncing sonar waves off the ocean bottom to determine depth. If a “ping” takes 1.534s to go down and return, how deep is the ocean beneath the ship? Assume that speed of the sonar wave is 1,473m/s. Slide3
The Position-Time graph (P-T
)
Slope is velocity (+/- speed)
y-intercept is position at time = 0
y = mx + b (algebraic relationship)distance = velocity*time + distanceo d = vt + do where v = constant (equation 1)Solving a practical problem…In constant motion Caution: in accelerated motionSlide4
The Velocity-Time Graph (V-T)
Slope = change in velocity / change in time which is acceleration
y-intercept equals velocity at time = 0
y = mx + b
velocity = acceleration*time + velocityov = vo + at (equation 2)Solving a practical problem…Slide5
The V-T graph details
Constant (non
-accelerated) motion
Slope = zero
Uniformly accelerated motionSlope constant, but does not equal zeroNon-uniformly accelerated motionSlope of tangent line at a given point gives accel.One cannot determine initial position based on a V-T graph. The area under a V-T graph is displacement.Slide6
Uniform Acceleration in P-T Graphs
The relationship between variables in uniformly accelerated motion.
d = d
o
+vot + ½ at2 (Equation 3)A practical example…We will address this subject matter further.Slide7
Kinematic Relationships
d = d
o
+
vt (constant velocity) (equation 1)v = vo + at (equation 2)d = do + vot + ½at2 (equation 3)Substituting t from equation 2 into equation 3 results in v2 – vo
2 = 2a(d-do) (equation 4)For one point of extra credit:Correctly demonstrate the derivation of equation 4.Turn in written proof on Friday at start of class.