Chapter 7
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Chapter 7

Course Number: PHYS 161,260,27, Spring 2008

College/University: Maryland

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CHAPTER 7 Conservation of Energy 1* What are the advantages and disadvantages of using the conservation of mechanical energy rather than Newton's laws to solve problems? Generally simpler, involving only scalars; cannot obtain some details, e.g., trajectories. 2 Two objects of unequal mass are connected by a massless cord passing over a frictionless peg. After the objects are released from rest, which of the...

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CHAPTER 7 Conservation of Energy 1* What are the advantages and disadvantages of using the conservation of mechanical energy rather than Newtons laws to solve problems? Generally simpler, involving only scalars; cannot obtain some details, e.g., trajectories. 2 Two objects of unequal mass are connected by a massless cord passing over a frictionless peg. After the objects are released from rest, which of the following statements are true? ( U = gravitational potential energy, K = kinetic energy of the system.) ( a ) U < 0 and K > 0 ( b ) U = 0 and K > 0 ( c ) U < 0 and K = 0 ( d ) U = 0 and K = 0 ( e ) U > 0 and K < 0 ( a ) 3 Two stones are thrown with the same initial speed at the same instant from the roof of a building. One stone is thrown at an angle of 30 o above the horizontal, the other is thrown horizontally. (Neglect air resistance.) Which statement is true? ( a ) The stones strike the ground at the same time and with equal speeds. ( b ) The stones strike the ground at the same time with different speeds. ( c )The stones strike the ground at different times with equal speeds. ( d ) The stones strike the ground at different times with different speeds. ( c ) Their kinetic energies are equal. 4 A block of mass m is pushed up against a spring, compressing it a distance x , and the block is then released. The spring projects the block along a frictionless horizontal surface, giving the block a speed v . The same spring projects a second block of mass 4 m , giving it a speed of 3 v . What distance was the spring compressed in the second case? K 1 = 1/2 mv 2 = 1/2 kx 2 ; mv 2 = kx 1 2 ; kx 2 2 = (4 m )(3 v ) 2 = 36 mv 2 = 36 kx 1 2 ; x 2 = 6 x 1 . 5* A woman on a bicycle traveling at 10 m/s on a horizontal road stops pedaling as she starts up a hill inclined at 3.0 o to the horizontal. Ignoring friction forces, how far up the hill will she travel before stopping? ( a ) 5.1 m ( b ) 30 m ( c ) 97 m ( d ) 10.2 m ( e ) The answer depends on the mass of the woman. ( c ) h = v 2 /2 g = 50/9.81 m = 5.1 m; d = (5.1/sin 3.0 o ) m = 97.4 m. 6 A pendulum of length L with a bob of mass m is pulled aside until the bob is a distance L /4 above its equilibrium position. The bob is then released. Find the speed of the bob as it passes the equilibrium position. 1/2 mv 2 = mg h ; h = L /4; v = ( gL /2) 1/2 . 7 When she hosts a garden party, Julie likes to launch bagels to her guests with a spring device that she has devised. She places one of her 200-g bagels against a horizontal spring mounted on her gazebo. The force constant of the spring Chapter 7 Conservation of Energy is 300 N/m, and she compresses it 9 cm. ( a ) Find the work done by Julie and the spring when Julie launches a bagel.

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Maryland - PHYS - 260
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Maryland - PHYS - 161,260,27
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David O'Brien Prelab #2t l m w2. tx = mgsin( ) ty = mgcos( ) Fx = tx = (mgsin( )*l 3. (sin( )- )/ .01 = 0% .1 = .1% .2 = .1% .3 =1.5% .4 = 2.6% .5 = 4.1% .6 = 5.9% .7 = 8.0% .8 = 10.3% .9 = 13.0% 1.0 = 15.9% 1.1= 19.0% 1.2 = 22.3% 1.3 = 25.9% 1.
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David O'Brien Prelab 7 1) pv = nRT =&gt; n = pv/RT n = (1.013x10^5)(100cm^3)/(300*8.3145) = 4061 moles 2) p1v1 = p2v2 20(30) = 10*p2 p2=60lbs/in2 3) Anytime the temperature drops below freezing.
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Maryland - PHYS - 161,260,27
CHAPTER5Applications of Newton's Laws1* Various objects lie on the floor of a truck moving along a horizontal road. If the truck accelerates, what force acts on the objects to cause them to accelerate? Force of friction between the objects and
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Maryland - PHYS - 161,260,27
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Maryland - PHYS - 161,260,27
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Maryland - PHYS - 161,260,27
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Maryland - PHYS - 161,260,27
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Maryland - PHYS - 161,260,27
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Maryland - PHYS - 161,260,27
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Maryland - PHYS - 161,260,27
CHAPTER24Electric Potential1* A uniform electric field of 2 kN/C is in the x direction. A positive point charge Q = 3 C is released fromrest at the origin. (a) What is the potential difference V(4 m) V(0)? (b) What is the change in the pot
Maryland - PHYS - 161,260,27
CHAPTER22The Electric Field I: Discrete Charge Distributions1* If the sign convention for charge were changed so that the charge on the electron were positive and the charge on the proton were negative, would Coulomb's law still be written the
Maryland - PHYS - 161,260,27
CHAPTER23The Electric Field II: Continuous Charge Distributions1* A uniform line charge of linear charge density = 3.5 nC/m extends from x = 0 to x = 5 m. (a) What is the total charge? Find the electric field on the x axis at (b) x = 6 m, (c)
Maryland - PHYS - 161,260,27
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Maryland - PHYS - 161,260,27
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Maryland - PHYS - 161,260,27
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Maryland - PHYS - 161,260,27
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Maryland - PHYS - 161,260,27
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Maryland - PHYS - 161,260,27
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Maryland - PHYS - 161,260,27
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Maryland - PHYS - 261
David O'Brien Section : 0106 Experiment #1 1. f=a-b df/da = 1 and df/db = 1 f = [(df/da*a)2 + (df/db*b)2]1/2 = sqrt(.52 + .52)=.7071 error = .2 +/- .7071 f = [1*(.5/11.5)2 + 1*(.5/11.3)2]1/2 = .0631 11.5/11.3 = 1.018 1.018 +/- .0631 2. (11.0+11.4+1