Phy 121
Your 'question form' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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I had some questions that are on the test that I do not understand. Problem 1
A person of mass 79 kf begins climbing a very high tower. The tower begins at the surface of the Earth, at a distance of 6400 km from the center, and rises to a position 3600 kilometers further from the center.
For each of the first three 1200 kilometer segments, determine the average of the initial and final gravitational forces encountered while climibing the segment. Give the total work required for each segment based on teh average of the initial and final forces for the segment. At an average power output of .62 watt/kg for 8 hours per day, how many days would be required to make the 3600 kilometere climb? For the first question would I just do 79 kg*9.8 m/s^2? Then i'm not sure how to get the other questions.
This question is addressed in the Introductory Problem Sets, Set 7, Problems 7 and 8, I believe. These were assigned in Assignments 27 and 28, if I recall correctly.
Note that virtually all the problems on your test will be from the Introductory Problem Set, with only some variation in the words and of course with different numbers. The solution process is given in those sets.
If you have questions about any of those solutions, I will of course be glad to clarify. However start with those posted problems.
Problem 2
A turbine rotates through 7.25 radians while accelerating uniformly from 9.99 radians/second to 14.99 radians/second. How long does this take, and what is the angular acceleration of the turbine?
I got that 7.25 radians would be 7 1/4 pi, but I wasn't sure how to get the acceleration, because it doesn't give the time.
you are given the angular displacement 7.25 radians, the angular acceleration 9.99 rad / sec and the final angular velocity 14.99 rad/sec.
Given displacement, acceleration and final velocity, you can use the fourth equation of motion to get the initial velocity. Then it's easy to reason out the time required.
The fourth equation for straight-line motion is
vf^2 = v0^2 + 2 a `ds.
For angular motion (i.e., rotational motion) we use omega for angular velocity, alpha for angular acceleration and `dTheta for angular displacement, and the equation becomes
omega_f^2 = omega_0^2 + 2 alpha `dTheta.
You know omega_f, alpha and `dTheta, so you can solve the equation for the initial angular velocity omega_0.
See the Introductory Problem Sets for a version of this problem, and for the Greek symbols.
I'll be glad to answer further questions.