Phy 101 Exam 3a 2008

Phy 101 Exam 3a 2008 - Wt e9 1 The asteroid Geographos has...

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Unformatted text preview: Wt e9 1. The asteroid Geographos has a radius of 2.4 x 10‘4 times the earth's radius, and a mass of 8.4 x 10‘12 that of the earth’s mass. How does the gravitational acceleration at its surface compare to the corresponding value of g on earth? a)2.4x10‘4g b)8.4x1o"2g‘ c)1.5x10"g d)3.5x10'3g e) none of these GmM Gm(8.4><10'12MEfim)m(8.4x10‘12)GMEarth _ Gco_ : F 2 i go os# _ w mgG mph (Rgeo)2 (2-4X10_4REanh)2 (2‘4X10—4)2(RE3”1‘)2 g Geographos = (8.4x10_]2) I: GMEmh (2.4><10“‘)2 (REanh)2]=1.5X10— gm memegélogqg 2. Tycho Brahe places a 6.0-m-Iong steel rod on a rock so that one end is under a baby moose weighing 2.0 kN. Mr. Brahe pushes down on the other end of the rod with a force of 400 N. and the moose is held in the air at rest. The rock was a) 1.0 mvfrom the moose b) 5.0 m from the moose c . m rom the person d) 6.0 m from the person 9) none of these Terrified baby moose l x I F. l i I TfLW = TCCW |Fl(6.0m—x) =|mg|(x) —> (400N)[6.0m —x) =(2000N)x 2400N - m - 400N(x) = 2000N(x) x =1.0m 3. The figure shows a planet in orbit around a star. If its speeds at the four points shown are V5_ VB, VC, 0 and VD. respectively, then a)vA<v3<vc<v b)VA)VB>Vc>VD VA>VB=D Vc d)VA<Vs=Vo<Vo B Per Kepler’s 2"CI Law, the velocity of the planet will be greatest when it is closest to the star, and least when at it's greatest distance. 4. The angular momentum about an axis through the center of a hoop (I = MR2) having a mass of 2.0 kg and a diameter of 2.0 m which is rolling down an incline at 2.5 We is a) 20 kg-m2i‘s w c) 8kg-m2ls d) none of these ifil=1|ai = MR2F1§3 = (2.0kg)(1.()m)2 =5-0kg-m2/S 5. A Christmas ornament made from a thin hollow glass sphere hangs from a small hook at its surface. it is observed to oscillate with a frequency of 2.50 Hz. What is the radius of the ornament? The moment of inertia of a hollow shpere of mass M and radius R about a point on its edge is gMRZ. a) 0.68 cm b) 0.92 cm c) 1.84 cm d) 2.39 cm e) 3.98 cm g m6 f 3s 3(9.8m/52) _ 20n2(2.50Hz)2 R = 0.0239 In 201:le = 6. Two straight inclined grooved tracks are lined up next to one another. Number 1 track is coated with a slippery film and number 2 track is not; otherwise. they are identical. Two steel balls are placed one on each track and released so that ball #1 slides down andw ball #2 rolls all the way. b) Ball #2 always wins 0) Bal 1 wins as often as ball #2 0) Both reach the bottom at the same time. e) Insuffient information to answer. At the bottom of the ramp: mgh=13mvl2 —) vI : 2gh mgh = émvg + go): V2 must be less than Vl ! 7. A fisherman fishing from a pier observes that the float on his line bobs up and down, taking 2.4 s to move from its hightest to its lowest point. He also estimates that the distance between adjacent wave crests is 48 m. What is the speed of the waves going past the pier? a) 3.0 mls b) 5.0 m/s d) 20 m/s e) 115 m/s v=7tf=§= 48m =10m/s T 2-2.4s 8. The moment of inertia of a uniform rod about its center is given by I: fiML? What is the kinetic energy of a 120—cm rod with a mass of 450 g rotating about its center at 3.033151%? b) 0700 J c) 2.10 J d) 4.20 J e) 5.19 J ilwz = l[iML2]u)2 = LU) 450kg-(12m)2](3 6rad/s)2 = 0 3501 R01. 2 2 12 24 ' ‘ ‘ ‘ 9. In many cartoon shows, a character runs of a cliff, realizes his predicament and lets out a scream. He continues to scream as he falls. If the physical situation is portrayed correctly, from the vantage point of an observer at the top of the cliff leaning over the edge, the pitch of the scream should be a) higher than the original pitch and constant. b) higher than the original pitch and increasing as he falls. lower than the original pitch and constant. : d) )ower than the original pitch and decreasing as he falls. It is impossible to predict. The pitch will go down when the source is moving away, BUT, when falling off a cliff (don’t try this at home), you will be accelerating due to gravity and so your velocity will be constantly increasing. 10. When the mass of a simple pendulum is tripled, the time required for one complete vibration _ _' creases by a factor of 2. b) increases by a factor of 3. c) as not change. d) decreases to one-third of its original value. '6 decreases to f of its original value. The period, T, of a simple pendulum is independent of mass. 11. A projectile is shot from the surface of the Earth by means of a very powerful cannon. If the projectile reaches a height of 35,000 m above the Earth's surface, what was the speed of the projectile when it left the cannon? a) 355 mis b) 505 m/s @827 mfs d) 710 mls e) 906 mls We begin by conserving energy! Eat surface : Eat max altitude %mv2 — % = 0 ._ Mimi (REal-th) (REai-th +11) 12. Two equal forces are applied to a door at the doorknob. The first force is applied perpendicular to the door; the second force is applied at 30° to the plane of the door. Which force exerts the greater torque? fie first applied perpendicular to the door b) the second applied at an angle 0) both exert equal non-zero torques d) both exert zero torques e) additional information is needed Torque is maximum when sin 9 = 90 ° . 13. A dumbbell-shaped object is composed of two equal masses, m. which are connected by a rod of negligible mass and length r. If I1 is the moment of inertia of this object with respect to an axis passing through the center of the rod and perpendicular to it and l2 is the moment of inertia with respect to an axis passing through one of the masses we can say that a) I1 = Iz. b) I1 > I2. @h < [2. 01) There is no way to compare l1 and I2. I2 : mr 14. Curve A in the figure at right represents - n underdamped situation. an overdamped situation. 0) a moderately damped situation. d) critical damping. e) a soaking wet situation 15. If head coach Randy Shannon were to say to President Shalala, "Either we spend a lot more money on our football program to make it more competitive, or we should scrap it altogether.”, he has committed which fallacy? a) the fallacy of division b the post hoc, ergo propter hoc fallacy c) the domino fallacy e fallacy of the false choice e) the professional suicide falla 16. The figure shows 3 masses connected by light (assumed massless) rods. The origin of the coordinate system is at the center of the mass labeled A, and the Z axis is perpendicular to the page. a) Calculate the moment of inertia about the X axis, and the force which would have to be applied to mass C (the force is directed straight into the page) to give the system an angular acceleration of 10 rad/32. 1x = mergc = (1.0kg)(4.0m)2 =16.0kg - m2 T : Ia = rF PEI—a = (16.0kg - m2)(10rad/sz) :40N r 4.0111 b) Calculate the moment of inertia about the Y axis, and the force which would have to be applied to mass B (again. the force is directed straight into the page) to give the system an angular acceleration of 1 rad/s2. 1y =mBr§B + mcrfm,B =(2.0kg)(3.0m)2 + (1.0kg)(3.0m)2 :27 kg -m2 (27kg-m2)(lrad/s)2 3.0m 0) Calculate the moment of inertia about the Z axis, and the force which would have to be applied to mass C (the force is directed perpendicular to the 5.0 m leg of the triangle) to give the system an angular acceleration of 5 radlsz. F: =9.0N IZ = merge =(1.0kg)(5.0m)2 + (2.0kg)(3.0m)2 =43.0kg - m2 1:=10L=rF F :12 = (43.0kg - m2)(5rad/sz) : 43N r 5.0m 7: 17. An airatrack cart is attached to a spring and completes one oscillation every —s. 2 At t = 0, the cart is pulled in the +x-direction a distance of 0.50 m and released. (Hint: set your calculator to radians”) a) Write an equation that describes the motion of the cart (namely its position x as a function of the time t). mfifilfls-l T T: -—S 2 211st x : Acos(o)t) = (0.50m)005[?] =(0‘50m)cos(4tS-l) b) What are the maximum velocity and acceleration of the cart? v = —A(osin (4t 8 '1) v =Am=(0.50m)[2—“] m T (0.50m)(4s—‘)=2.0m/s a = —Ac)2 cos(4ts“l) am = A032 = (0.50m)(4s'1 )2 = sum/32 4 c) What are the position, velocity and acceleration of the cart at t = —Rs x = Acos((ot) = [0.50m)cos(4s'l ~t) = (0.50111)cos[45'l = —0.25m V=—Ao)sin(o)t)=—(0.50m)(4s'l)sin[4s‘l -i}s]=1.73m/s a : —Ar.o2 cos(cot) = —(O.50m)(4s_l )2 cos[43_l = 4.0m/s2 ...
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This note was uploaded on 10/13/2011 for the course PHY 101 taught by Professor Ashkenkai during the Spring '08 term at FIU.

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