course Phy 241 βm┝ODͩГֶɝassignment #005
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05:22:36 Intro Prob 6 Intro Prob 6 How do you find final velocity and displacement given initial velocity, acceleration and time interval?
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RESPONSE --> First find `dv by multiplying a by `dt. Once you find the `dv you can add that to the initial velocity to get the final velocity. To find the `ds find the average velocity by adding the final and initial divide by two then multiply by `dt.
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05:22:50 ** To find final velocity from the given quantities initial velocity, acceleration and `dt: Multiply `dt by accel to get `dv. Then add change in velocity `dv to init vel , and you have the final velocity**
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RESPONSE --> ok
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05:24:15 Describe the flow diagram we obtain for the situation in which we know v0, vf and `dt.
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RESPONSE --> With v0 and vf we can obtain average velocity. With average velocity and `dt we can get `ds. With v0 and vf we can get the `dv and with `dv and `dt we can get the average acceleration.
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05:24:37 ** The flow diagram shows us the flow of information, what we get from what, usually by combining two quantites at a time. How we get each quantity may also be included. From vf and v0 we get `dv, shown by lines from vf and v0 at the top level to `dv. From vf and v0 we also get and vAve, shown by similar lines running from v0 and vf to vAve. Then from vAve and `dt we get `ds, with the accompanying lines indicating from vAve and `dt to `ds, while from `dv and `dt we get acceleration, indicated similarly. **
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RESPONSE --> ok
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05:24:47 Principles of Physics and General College Physics Students: Prob. 1.26: Estimate how long it would take a runner at 10 km / hr to run from New York to California. Explain your solution thoroughly.
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RESPONSE --> n/a
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05:24:50 It is about 3000 miles from coast to coast. A km is about .62 mile, so 3000 miles * 1 km / (.62 miles) = 5000 km, approximately. At 10 km / hr, the time required would be 5000 km / (10 km / hr) = 500 km / (km/hr) = 500 km * (hr / km) = 500 (km / km) * hr = 500 hr.
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05:27:52 All Students: Estimate the number heartbeats in a lifetime. What assumptions did you make to estimate the number of heartbeats in a human lifetime, and how did you obtain your final result?
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RESPONSE --> I assumed that a person would average 60 beats per minute and that an average lifetime was about 75 years. I multiplied 60 x 60 x 24 x 365 x 75=about 2.4 x 10^9
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05:28:19 ** Typical assumptions: At 70 heartbeats per minute, with a lifetime of 80 years, we have 70 beats / minute * 60 minutes/hour * 24 hours / day * 365 days / year * 80 years = 3 billion, approximately. **
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RESPONSE -->
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05:31:26 University Physics Students Only: Problem 1.52 (i.e., Chapter 1, Problem 52): Angle between -2i+6j and 2i - 3j. What angle did you obtain between the two vectors?
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RESPONSE --> I used the scalar product to obtain an angle of -22 degrees.
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05:41:12 ** For the given vectors we have dot product =-2 * 2 + 6 * (-3) = -22 magnitude of first vector = sqrt( (-2)^2 + 6^2) = sqrt(40) magnitude of second vector = sqrt( 2^2 + (-3)^2 ) = sqrt(13) Since dot product = magnitude of 1 st vector * magnitude of 2d vector * cos(theta) we have cos(theta) = dot product / (magnitude of 1 st vector * magnitude of 2d vector) so that theta = arccos [ dot product / (magnitude of 1 st vector * magnitude of 2d vector) ] = arccos[ -22 / ( sqrt(40) * sqrt(13) ) ] = arccos ( -.965) = 164 degrees, approx.. **
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RESPONSE --> Ok I do know how to do this. I assumed that the scalar product was equal to the angle between A and B because page 26 reads that ""The scalar product gives a straightforward way to find the angle theta between any two vectors A and B whose components are known. It makes sense that you would need to do something else because earlier in the text it states that ABcos(theta) does equal the dot product, not theta alone.
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05:41:17 Add comments on any surprises or insights you experienced as a result of this assignment.
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RESPONSE -->
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05:41:24 ** I had to get a little help from a friend on vectors, but now I think I understand them. They are not as difficult to deal with as I thought. **
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RESPONSE -->
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