Class 110921
These tasks are due by Wednesday of next week. However it is recommended that you take a good look at the Introductory Problem Sets and the Major Quiz before Monday's class.
You should be prepared for the Major Quiz by the middle of next week. Click on the Tests link to access a variety of Major Quizzes.
Note also the links
On your Physics I homepage you will see a blue button at the top, entitled 'Prob Sets'. You should review all the information provided in Problem Sets 1 and 2. There's nothing in those problem sets you shouldn't already know, but you will profit from seeing how the solutions are presented there. This will help you on the Major Quiz.
A direct link to the Introductory Problem Sets is
Text Assignment: Read through Chapters 1 and 2, Chapter 4 Sections 1-6 (Phy 201), Chapter 4 Sections 1-5 (Phy 231 and 241), Chapter 6 Sections 1-6 (Physics 201), Chapter 6 (Phy 231 and 241). Make notes about what you recognize from the work you have been doing, get used to the book's notation, and skim over things you don't recognize ('skim over' doesn't mean 'skip', to skim is to read over to get a general idea but don't try to understand all the specific details).
Answer and submit the following questions, indicating in each case how you found your answer:
`q001. The meter, the kilogram and the second are the basic SI units (SI stands for 'standard international').
Velocity is the rate of change of position with respect to clock time. What therefore are the SI units of velocity?
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Acceleration is the rate of change of velocity with respect to clock time. What therefore are the SI units of acceleration?
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A Newton is the SI unit of force. Force = mass * acceleration. In terms of kg, meters and seconds, what therefore are the units of of force? The resulting units are the units of a Newton.
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A Joule is the SI unit of work. Work = force * displacement. In terms of kg, meters and seconds, what therefore are the units of work? The resulting units are the units of a Joule.
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Power is measured in watts. A watt is a Joule per second. What therefore are the fundamental units equivalent to a watt?
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What are the fundamental units equivalent to Newtons * meters? What quantity would be expressed in these units?
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What are the units of kinetic energy?
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`q002. Sketch an object on inclines of 10, 20 and 30 degrees; you will have three sketches. For each incline, sketch the arrow indicating the force exerted on the object by gravity (for each incline we'll refer to this as the 'first arrow'). For each sketch, construct the arrow which represents the component of the gravitational force parallel to the incline (you do this by projecting the arrow at a right angle onto a line parallel to the incline, as we did in class).
For each incline, estimate the length of this arrow as a percent of the first. Give your three estimated percents:
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`q003. My truck has a mass of about 1400 kg. It reaches the part of the road which has a nearly constant incline, in front of VHCC, at a speed of 5 meters / second in the direction down the incline. In 12 seconds its speed has increased to 10 meters / second.
What is my acceleration on that incline?
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What is the net force on the truck as it coasts down that incline?
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What is the change in its kinetic energy as it coasts down the incline?
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If friction exerts a force opposite to my direction of motion, with the magnitude of the frictional force equal to 2% of the force exerted by gravity on the truck, then during this interval how much work is done on the truck by the frictional force?
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The net force on the truck is the combination of the frictional force, and the component of the gravitational force which acts in the direction down the incline. What therefore is that component of the gravitational force, and what percent is this of the total gravitational force pulling the truck toward the center of the Earth?
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Make a reasonably accurate sketch depicting the incline, the truck, the gravitational force and its component along the incline.
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`q004. In the preceding, suppose that the direction down the incline is positive. The 5 meter / second initial velocity is therefore positive, and we would write v_0 = + 5 m/s. If the force of air resistance on the car was 2 kg m/s^2, then since that force is directed up the incline, it would be represented as -2 kg m/s^2.
Give each of the following, including its sign, its numerical value and its units:
The final velocity of the truck.
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The change in the kinetic energy of the truck.
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The acceleration of the truck.
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The force of friction on the truck.
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The component of the gravitational force parallel to the direction of the incline.
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The net force on the truck.
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`q005. Suppose the truck coasts up the incline, starting at a velocity of 15 m/s, and continues until its velocity has decreased to 10 m/s. The frictional force still has a magnitude equal to 2% of the total gravitational force on the truck.
Let the direction down the incline be positive.
Give each of the following, including its sign, its numerical value and its units:
The final velocity of the truck.
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The change in the kinetic energy of the truck.
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The force of friction on the truck.
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The component of the gravitational force parallel to the direction of the incline.
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The net force on the truck.
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The acceleration of the truck.
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`q006. This problem requires that you use the four equations of uniformly accelerated motion. If the truck reaches an incline on which its acceleration is .5 m/s^2, with velocity 10 m/s (both velocity and acceleration in the same direction), then how long will it take to reach a point 200 meters down the incline and how fast will it be moving at that point? You will need to carefully identify which of the quantities v0, vf, ds, dt and a are given. Then you should jot down the four equations of uniformly accelerated motion and select the one that most easily gives you additional information, and proceed from that point.
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`q007. This problem is fairly challenging. I expect all University Physics students to get it, and hope that at least some General College Physics students will also get it despite the fact that it's probably at least a little bit too challenging for this point of the course.
Suppose the truck is moving up the incline, on which its acceleration is .7 m/s^2 down the incline. It passes you moving at 12 meters / second, and then passes your friend, who is standing 16 meters up the incline from you.
How long does it take the truck to travel the intervening distance?
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How far up the incline does it go before coming to rest?
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If it then coasts back down the incline, accelerating at .5 m/s^2, how long will it take to travel from the position of your friend to your position?
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University Physics Students:
`q008. Describe the experiment you did in lab today. Describe the setup of the experiment, what you measured, and how you interpret your results.
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`q009. The velocity of an object on a certain nonconstant incline is given by the function
v(t) = .03 m/s^4 * t^3 - .2 m/s^3 t^2 + 3 m/s^2 * t + 5 m/s.
Sketch a graph of this velocity function and estimate the displacement of the object between t = 5 sec and t = 10 sec.
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What is the function that represents the object's acceleration a(t)?
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The object has mass 7 kg.
What is the momentum of the object at t = 5 sec, and at t = 10 sec?
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What is the function that represents the net force on the object as a function of time?
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Sketch a graph of this force function between t = 5 sec and t = 10 sec, and determine the corresponding area beneath the graph.
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What is the meaning of this area? If you can, state how it is related to certain other quantities calculated above.
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