Physics I Class 111107
Notes from 111102 were posted incorrectly and were not available until 111106. You should report your data from last week's experiments promptly. The remainder of that assignment will not be due until 11/14/11, but you are encouraged to complete it before then.
force vectors for 3-rb experiment
ball on ramp: translational KE change vs. PE change; however there's not much energy loss due to rolling friction (put limits on this by timing ball up and down ramp, using comparisons with other known times etc.)
transition to sliding friction
... rotating strap or disk with curved ramp, marbles or steel balls ... or steel balls spaced from a magnet (rotational speed to break free)
... sample tests ... write down everything you know that you think might be relevant ...
... collision experiment
... restitution
... elastic, inelastic collisions (relative velocity; ball and marble from opposite directions ... )
... horiz range of ball, grav sim,
... energy conservation of ball on ramp; transition to sliding ...
... angular momentum, vectors, conservation
... symbolic representations
... umwrap chain around rotation wheel
... rotating strap or wheel speeds up then coasts to rest ... frictional torque ...
You were asked in class last week to have problems as assigned on 10/24/11 written out and ready for my scrutiny. If you didn't have it today, be sure to have it Wednesday.
Report your data on the collision experiment done in class today. Report in a readable format, including explanations and descriptions, and putting numerical data into easily-read table form.
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University Physics students report your data on coefficient of restitution and the radius of the circle described by the contact point of the ball and the ramp:
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Collision experiment:
Report your data, including a description and documentation sufficient for later reference:
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All students note that the remaining problems in the Introductory Problem Sets should be accessible to you, and that these problems often appears on tests. You should be sure you understand all of the Introductory Problem Set problems and their solutions.
Text problems:
You should begin work on these problems by reading them and making preliminary notes. Your preliminary notes should indicate what concepts and definitions you think might be relevant to each, plus sketches, plan of attack, etc.. Leave yourself ample room to complete your work on each problem. You will be asked to allow the instructor to view your preliminary notes on Wednesday of next week.
General College Physics (note that if you have trouble with the assigned problems, which are all level II, you should first work as many Level I problems as necessary):
Chapter 5: Problems 6, 18, 36, 38, 50
Chapter 7: Problems 28, 32, 36
Chapter 8: Problems 12, 20, 24, 34, 48, 54, 62
Chapter 9: Problems 6, 16, 20, 32, 36
Chapter 11 (sections 1-4 only): Problems 4, 8, 14, 16, 24, 32
University Physics:
Chapter 3: Problems 72, 80
Chapter 9: Problems 64, 66, 76, 84, 92, 98
Chapter 10: Problems 54, 64, 74, 88, 94
Chapter 11: Problems 44, 46, 50, 58, 62
Chapter 12: Problems 50, 56, 62, 70, 76
Chapter 13: Problems 64, 70, 76, 84
Questions:
`q001: A rubber band chain is stretches from the point (10 cm, 5 cm) to the point (50 cm, 35 cm). The tension vs. length graph for this chain has horizontal intercept 42 cm and slope .15 N / cm.
What is the length of the rubber band chain?
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What therefore is its tension?
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What are the x and y components of a vector from the (10 cm, 5 cm) point to the (50 cm, 35 cm) point?
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What therefore is the length of this vector?
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What do you get if you divide this vector's x and y components by its length?
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The results of the preceding are the x and y components of the unit vector in the direction of the rubber band. If you multiply these components by the tension force, you get the x and y components of the tension force vector. What are these components?
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What therefore are the magnitude and angle of the tension force vector?
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How much work would have to be done to extend the rubber band one more centimeter?
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1q002. If the rubber band chain in the preceding suspends a 40 gram mass, holding it in equilibrium against the force of gravity on the mass, then how long will the chain be?
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If the 40 gram mass is pulled down until rubber band chain is 50 cm long, and the mass is released, what will be the net force on the mass the instant after release?
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In the preceding, with what force was the mass pulled down before being released?
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How much work will be done by the tension force on the mass as it returns to its equilibrium position?
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If the rubber band tension was conservative, what would be its velocity upon return to equilibrium?
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`q003. A 40 gram mass is dropped from rest at a height of 2 meters above the floor. What is its momentum just before it strikes the floor?
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How fast is the mass going when it first loses contact with the floor on its rebound, given that it rebounds to a maximum height of 1.5 meters?
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What therefore is its momentum when just after leaving the floor on its rebound?
By how much does its momentum change during the interval from just before contacting the floor to just after leaving the floor on its rebound? Be sure to choose a positive direction and answer relative to that direction.
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`q004. A steel ball 25 mm in diameter has mass about 70 grams. A point on that ball which lies 9.9 mm from its axis of rotation is moving in a circular path about that axis, traveling at 30 cm / second.
How many times does that point go around the circle in a second?
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What is its angular velocity in radians per second?
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What is the moment of inertia of the ball?
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The angular velocity of the steel ball about that axis is the same as that of the point. What therefore is the angular kinetic energy of the ball?
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`q005. If you are in a car traveling at 70 mph behind another car traveling in the same direction at 60 mph, then your velocity relative to that car is 10 mph in your direction of motion. If you are traveling at 70 mph and another car is traveling at 60 mph in the opposite direction, then your velocity relative to that car is 130 mph in your direction of motion (and its velocity is -130 mph in your direction of motion).
A ball moving at 50 cm/s approaches another ball moving toward it at 20 cm/s. The balls collide and both balls reverse their directions, the first moving at 10 cm/s while the second moves at 60 m/s.
Before collision, what is the velocity of the first ball relative to the second?
After collision, what is the velocity of the first ball relative to the second?
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What is the magnitude of the velocity change of the first ball, and what is the magnitude of the velocity change of the second?
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Which ball do you conclude had the greater mass?
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While they were in contact, which ball exerted the greater force on the other? If you can't answer this question as it is posed, state why.
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Key words, phrases etc. f rom assigned University Physics problems
Ch 3
Problem 72: … a rocket traveling vertically upward launches a second rocket …
Problem 80: “Raindrops”… train’s velocity … raindrops falling vertically …
Chapter 9
Problem 64: Sketch a wheel in the plane of your paper … select a point on the rim …
Problem 66: A roller in a printing press turns through an angle …
Problem 76: A thin uniform rod … bent at its center into a V shape …
Problem 84: Exactly one turn of a flexible rope … wrapped around a uniform cylinder
Problem 92: (includes picture of pulley, cylinder and box…) … the cylinder and pulley turn without friction about a stationary horizontal axis…
Problem 98: Neutron stars and Supernova Remanants: The Crab Nebula …
Chapter 10
Problem 54: An experimental bicycle wheel is placed on a test stand …
Problem 64: (includes sketch of block on incline, pulley at top) A block … slides down a surface … coefficient of kinetic friction is …
Problem 74: (includes picture of an irregular hillside-type path) A uniform marble rolls without slipping down the path shown …
Problem 88: The solid wood door of a gymnasius … hinged on one side …
Problem 94: A uniform wire of mass … is cut, bent, and the part soldered together …
Chapter 11
Problem 44: A pickup truck has a wheelbase of … box … placed on the tailgate …
Problem 46: A thin uniform metal rod is bent into three perpendicular segments …
Problem 50: A museum of modern art it displaying an irregular … sculpture … from two vertical wires
Problem 58: A uniform drawbridge must be held at …
Problem 62: (includes picture of two spheres suspended by wires from ceiling) A holiday decoration consists of two tiny glasss spheres suspended at …
Chapter 12
Problem 50: A uniform sphere … held with its center at the origin …
Problem 56: A landing craft … in circular orbit above the surface of a planet …
Problem 62: Your startship … lands on the mysterious planet …
Problem 70: Find the gravitational force that the Earth exerts on a … mass if it is placed …
Problem 76: As Mars orbits the Sun in its elliptical orbit …
Chapter 13
Problem 64: Four passengers with combined mass… compress the springs of a car …
Problem 70: A rocket is accelerating upward … from a launchpad on Earth … Inside a small ball … hangs …
Problem 76: A … bolt moves with SHM that has an amplitude of …
Problem 84: For a certain oscillator the net force on a body with mass …