course Phy 121 ?????????????assignment #005005. `query 5
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17:20:03 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 --> I would use the equation vf = v0 + 2`dt to get final velocity. Once I had that I would use the equation `ds = (vf+v0)/2 * `dt. confidence assessment: 3
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17:22:18 ** 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 --> I guess this is more of the direct reasoning approach. I can see how it's easier to see it this way rather than using just the formulas. self critique assessment: 2
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17:26:07 Describe the flow diagram we obtain for the situation in which we know v0, vf and `dt.
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RESPONSE --> `dt, v0 and vf are on the top level. `dv and vAve are connected to vf and v0 on the second level. Also on the second level is accel. connected by `dt and `dv. vAve and `dt connect to get `ds. confidence assessment: 3
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17:26:27 ** 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 self critique assessment: 3
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17:34:57 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 --> I first estimated that the US is about 3500 miles across. Then I converted this to kilometers by multiplying 3500 by 1.61 to get 5635 km. Then if she is running at 10km/hr, it's going to take her about 563.5 hours, or 23 days to get across the US. confidence assessment: 3
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17:35:20 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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RESPONSE --> I guess I overshot how long the US was. self critique assessment: 3
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17:39:31 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 --> The average number of heartbeats in a minute is 75. So in 1 hour that will be 4500 heart beats. In one day that would be 108000 beats. The average person lives to be about 80, depending on whether you are male or female. If you live to be 80, then you have lived 29200 days. If your heart beats 108000 times a day for 29200 days, then your heart will have beaten approximately 3.15 x 10^9 times. I think this is a fair estimate for the average person considering the down time your heart is beating less and the times during activity when it is beating more. confidence assessment: 3
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17:39:41 ** 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 --> ok. self critique assessment: 3
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17:39:47 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 --> confidence assessment:
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17:39:50 ** 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 --> self critique assessment:
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17:40:25 Add comments on any surprises or insights you experienced as a result of this assignment.
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RESPONSE --> I really got a better understanding of how to solve for one thing when given other things. It was kind of like solving a puzzle. self critique assessment: 2
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