EXAM 3                      December 3, 1997                          PHYS 207

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If you need a constant not given here or do not understand a problem, please ask me about it.
No notes, books, etc. may be used during this exam.

g = 9.8 m/sec2Radius of the earth = 6.38 x 106 m The mass of the electron is 9.11 x 10-31 kg.
For all problems, place the equations representing the physics principles you are using in the box on the page. You may use the general form of the equation or the form you get applying the principle to the problem at hand. If no diagram is applicable to a problem, write "none" in the diagram section. 1. (10 points) Write down the equations or general principles generally used to solve problems involving
(a). collisions, and (b). equilibrium.

(c). How do you recognize that the problem you are working with is a collision problem?
(d) How do you recognize an equilibrium problem?

2. (30 points; from homework)
Diagram [complete as necessary]
A uniform, square sign of mass M, and side h, is hung from a horizontal rod of length L as shown in the diagram. A cable is attached to the end of the rod and to a point a distance W above the point where the rod is fixed to the wall. What is the tension in the cable and the horizontal and vertical components of the force exerted by the wall on the rod?

Principles:
















3. (30 points)
Imagine a universe in which the law of gravitation has the inverse-first-power form

F = - [H M m / r] 1r

where H is an experimentally-determined constant.

(a) Show that the speed of a planet in a circular orbit is independent of the radius r of the orbit.

(b) Show that in such a universe Kepler's third law would take the form

r / T = constant

where T is the period of the orbit.

Diagram:

Principles:











4. (30 points) A ring of mass M and radius R lies at rest on its side on a frictionless table. It is pivoted to the table at its rim. A bug of mass m starts walking around the ring with speed v, starting at the pivot. What is the rotational velocity of the ring when the bug is directly across the ring from the pivot?

Diagram:
Principles:











Use this page if necessary to continue any of the problems. Be sure to label the problem number.