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PHYSICS 477 FINAL EXAMINATION

This exam is due no later than 13 May 2005

You may also submit the lesson plan on 13 May 2005

Exams may be emailed to dslavsk@luc.edu, faxed to 773-508-3506, or mailed to David Slavsky/Center for Science and Math Ed/Loyola University/6525 N. Sheridan Rd/LSB 431/Chicago IL 60626.

All questions are worth ten points unless otherwise noted. Answers should be complete, calculations need to be worked out in detail.

1. Assume the orbit of the Earth around the sun is a perfect circle (it is not, differing from a circle by about 3%), but for this problem assume that. Look up data on line or in appropriate physics or astronomy books to determine the average speed of the Earth in its orbit. Give your answer either in miles/sec or km/sec, but not in any other unit. [Hint: Recall that the circumference of a circle is 2 pi R where pi is 3.14 and R is the radius of the circle.] You must show your calculations; you may look up the values of the orbital data needed to do the calculation, but you must do the calculation and not just quote the final result.

2. In fact, the orbit of the Earth is not exactly circular, differing by about 3% from our closest approach in January to our most distant in July. When during the year would the Earth have the greatest gravitational attraction to the Sun? To be more numerical, at our closest to the Sun we are approximately 91.5 million miles from the sun; at our most distant, we are about 94.5 million miles. What is the ratio of gravitational force we feel from the sun at these two times, i.e., what is the ratio of force at 91.5 million miles to the force at 94.5 million miles. Show all your work so I can follow your logic explicitly

3. Explain how an inclined plane or ramp acts as a machine. Suppose I need to lift a 1000 pound mass by rope to a height of 5 meters. However, my strongest rope can only support a force of 250 pounds. How far up a ramp would I have to pull this weight (pulling the weight by this rope) to raise it 5 meters above the ground and not break the rope? Show all work.

4. While in Home Depot recently, I overheard a father explaining to his child child "and the voltage �." through the circuit and causes..." Is this accurate language to use in describing the nature and behavior of voltage? If not, how should one describe voltage? Finally, what is it that we say "flows" through a circuit?

5. Birds are often seen perched on high voltage power lines, and do not suffer any physical damage despite sitting on wires of high voltage. Explain, using the concepts you have learned in this course, why they can do this without harm? (The answer does not involve any special property of birds.)

6. Suppose we set up a simple series circuit with 3 D Cell batteries (each D cell has 1.5 V) and two simple light bulbs each having a resistance of 50 O. A) Draw a simple diagram representing this circuit. B) What is the total current flow through this circuit? C) Suppose I add a 33O resistor in series to this circuit, diagram now how this circuit would look. D) What is the current in your circuit now. Show all work. [20]

7. A danger that faces farmers is that electrical charge can build up inside corn (or wheat) silos and cause explosions in the silo. Consider a silo, initially stationary with respect to the earth, that explodes in such a way, sending out fragements of the silo in all directions. A local engineer is able to reconstruct the mass and velocity of each of the many fragments that erupted outward. He/she then calculated the mass times velocity of each and every fragment that exploded and then summed all the products of mass times velocity. What numerical answer did he/she obtain at the end of this arduous task? Explain why this is the correct answer.

8. A block of mass 10 kg is initially moving at a speed of 10 m/s along a smooth, frictionless surface. The block then moves onto a rough horizontal surface of coefficient of friction equal to 0.3. Answer the following questions: Showing clearly how you arrive at all answers.
a) What is the normal force acting on the block. What is the total friction force acting on the block?
b) What is the acceleration of the block on the rough surface?
c) How far will the block travel on the rough surface before coming to rest?
d) How long (in time) will the block travel on the rough surface before coming to rest?
[show all work, each part worth 5 pts, the whole question is worth 20 pts]

9. A block slides down a plane of one meter in a time of two seconds.
a) What is the average speed of the block in this trip?
b) What is the final instantaneous speed at the end of the meter trip?
c) What is the average acceleration for the trip?
d) If this block could travel at this acceleration down a ramp for a time of four seconds, how far would it travel in four seconds?
[show all work/5 pts each part, 20 pts total question]

10. An object of mass 5 kg is dropped from rest from a height of 180 m. (Assume that g has a value of 10 m/s/s for this problem).
a) How long will it take for the object to hit the ground?
b) What will its speed be the instant before impact?
c) If this object hits a solid surface and comes to rest in 0.01 secs after initial impact, how much force acted to stop its motion?
d)If the object hit a more cushioned surface and took 0.1 sec to come to rest after initial impact, how much force acted to stop its motion?
[show all work/20 pts each question]

11. Two children are on opposite sides of a seesaw. One child, with mass 50 kg, is 4 ft from the fulcrum. If the other child is 25 kg, how far from the fulcrum must this child sit for the two to be balanced? Show all work.

David B. Slavsky
Loyola University Chicago
Cudahy Science Hall, Rm. 404
1032 W. Sheridan Rd.,
Chicago, IL 60660
Phone: 773-508-8352
E-mail: dslavsk@luc.edu

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