Assignment #3 Reading, Objectives, & Problems
A. Availability and Due Dates
|
Assignment #3 is available Tuesday, September 21, 2004. The target date for its successful completion is Thursday, September 30, 2004. In any event, all of the Type A problems from Assignment #3 must be successfully completed and turned in by 5:00 pm on Friday, October 15, 2004. If this requirement is not met, the student will not be allowed to take Quiz 2, to be given in class on Tuesday, October 19, 2004. |
B. Reading
|
As preparation for completing the problems in Assignment #3, read Chapters 6 & 7 in Cohen's The Fundamentals of College Physics, Volume IA. |
C. Objectives
In addition to the Objectives listed on Assignments #1 and #2, after completing Assignment #3, the student should
|
Be able to explain the microscopic origin of forces due to air pressure. Be able to explain why such forces are typically unimportant in influencing the way in which objects fall, at least when the speeds of the objects are slow. |
|
Know what is meant by the term air resistance, and be able to explain its microscopic origin. Realize that air resistance becomes more and more important as objects speed up, and be able to explain why. |
|
Know Newton's Universal Law of Gravitation. Further, the student should be able to apply this law in all physical situations in which it is relevant. |
|
Realize that there exists an attractive gravitational force between all massive bodies, and realize also that this force does not require contact between the bodies. |
|
Know the approximate value of G, the gravitational constant. For this to be meaningful, the student must obviously also know the units of G. |
|
Know the simplified form for the gravitational force acting on objects near the surface of the Earth. Know the value (and units!) of the constant g that appears in this form, and be able to express g in terms of G and the mass and radius of the Earth. |
|
Be able to calculate the acceleration due to gravity near the surface of any object [planet, moon, etc…], given the mass and radius of the object. |
|
Be able to explain why the gravitational acceleration of freely falling objects near the surface of the Earth is the same for all objects [in the absence of air resistance]. |
|
Be able to explain why the gravitational force acting on objects near the surface of the Earth is very nearly independent of height. |
|
Know what is meant by the term "Tension". Realize that tension is not a fundamental force, but rather can be understood in terms of the fundamental force of electromagnetism. Be able to identify the presence of tension forces in physical problems. |
|
Know what is meant by the term "Normal Force". Realize that normal forces are not fundamental forces, but rather can be understood in terms of the fundamental force of electromagnetism. Be able to identify the presence of normal forces in physical problems. |
|
Realize that the adjective "Normal" in the term "Normal Force" means "perpendicular" and understand why this adjective is appropriate. |
D. Type A Problems
[1] Problem 6.5 on p. 143 of Cohen. Do part (a) only, and assume that the mass of the person is 70 kg.
[2] A block having mass 2 kg. is placed on a frictionless surface that is inclined at an angle of 40° with respect to the horizontal. Determine (a) the acceleration of the block down the plane, and (b) the magnitude of the normal force between the block and the plane. Highly recommended fist step: Draw a free body diagram for this situation.
[3] The gravitational force between two massive objects is 100 N when their centers are separated by a distance of 2 km. How far apart would the two have to be in order for the gravitational force between them to be only 50 N?
[4] Suppose that a certain rope will break if the tension in it exceeds 250 N.
(i) Show that a 10 kg object may safely be suspended from this rope.
|
(ii) The rope is now used to accelerate the object upwards. Determine the maximum acceleration that may be achieved for the object without breaking the rope. |
[5] In order to pull a 70 kg sled across a frictionless surface, a rope is attached to the front of it. Determine the acceleration of the sled when:
(a) The rope is pulled horizontally and has a tension of 100 N.
|
(b) The rope is oriented at an angle of 30° above the horizontal, but still has a tension of 100 N. |
E. Type B Problems
[6] "The gravitational force on a 20 kg object is twice that on a 10 kg object, according to Newton's Universal Law of Gravitation. Therefore, the 20 kg object should fall twice as fast when released near the surface of the Earth."
Correct the statement above.
[7] Imagine a fictitious planet with mass 8 times that of the Earth, and a radius twice that of the Earth. Determine the acceleration due to gravity, "g", on the surface of this planet.
[8] It is often said that gravitation is a "fundamental force", while Tension and Normal forces are not "fundamental". Why is it that we do not view the Tension and Normal forces as fundamental?
[9] Problem 6.1 on p. 143 of Cohen.
[10] Problem 6.4 on p. 143 of Cohen.
[11] Problem 6.6 on p. 143 of Cohen.