Written homework #7 is due at the beginning of class on Friday March 27. Online homework #7 is due by Tuesday March 31 at 8 am.
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26 thoughts on “Homework #7”
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For written homework #7, part C, is it a diagram alone that you are looking for?
You need to draw a free-body diagram showing the forces acting on the satellite but also show that the forces exerted by the Earth and the Moon are equal in magnitude.
How do you want us to show that the forces are equal? Through the diagram or through some type of equation? or both…
You need to calculate the magnitude of each of those two forces and show they are equal.
I should also mention that for the written homework, you are not given the mass of the satellite. So to prove the forces are equal, you should take the ratio between the two forces acting on the satellite.
For part C of the written homework do we need to know whether d is the distance from the surface of the moon to the surface of the earth or should we assume that it is center to center?
In part C, is the distance, d, the distance between the centers of the Earth and moon, or the surfaces?
The distance d is from the center of the Earth to the center of the Moon (the radii of the Earth and Moon are quite small compared with this distance anyway).
Is the gravitational acceleration expressed by the unit N?
The gravitational acceleration should have the same unit as any other acceleration, so it should have units of m/s^2. The Newton (N) is a force unit.
Do we need to convert km into m for parts a and b?
In part c, when calculating the forces acting on the satellite, should the distance between the moon and the earth be converted from meters to kilometers? When I do this a get a large percent error in my final answer.
in part c how do you calculate the magnitude of the forces acting on the satellite?
Converting the distances in m is required since the constant G is given in those units.
Magnitude of the forces are given by Newton’s universal law of gravitation, see lecture notes or the textbook.
I was wondering whether we are able to complete all of the online hw #7 at this point or if we still need monday’s lecture?
There is one problem in the online homework #7 that requires the calculation of the center of gravity. I just ended on that in today’s lecture and will say a few more things about it on Monday. However, since this is a “tactics box” type of problem, it teaches you how to go about calculating the center of gravity, exactly what I showed in my last slide today. I plan to work out one example problem on Monday on that topic.
I’m having trouble with the last three problems for the online homework #7, I feel like we haven’t gone over problems in lecture similar to those to help figure it out and it makes it harder that there are no hints to guide you either. Will you be going over anything in lecture Monday to help for those last three problems?
I am indeed planning to spend a bit of time tomorrow in the lecture to cover a problem similar to those three.
how do you approach problem 7.9 in the online hw?
I am also having trouble approaching problem 7.9
Problem 7.9 is a lot simpler than it looks. Most of the information about the door is not needed. You simply need to figure out what minimum force is needed to produce a torque as big as that exerted by the door closer.
How do we solve part c in problem 7.1 if we are not given the mass of any of the three objects? I think I must be missing something here but I just keep staring at the problem and nothing has come to my attention.
I assume you mean the Tactics Box 7.1 problem. The solution is almost identical to the center of gravity problem I discussed in class this morning.
How do you approach problem 7.20
You need to compute the torque produced by the weight of the beam (considering that the weight acts at the center of gravity of the beam, i.e. its mid-point) and by the weight of the construction worker (considering that its weight acts at the end of the beam).