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Unformatted text preview: » 777 77 77777 Instructor(s): Saab/Sabin . PHYSICS DEPARTMENT
PHY 2048 Exam 2 October 26, 2010 Name (print, last ﬁrst): Signature: On my honor, I have neither given nor received unauthorized aid on this examination. YOUR TEST NUMBER IS THE 5DIGIT NUMBER AT THE TOP OF EACH PAGE.
(1) Code your test number on your answer sheet (use lines 76—80 on the answer sheet for the 5digit number). Code your name on your answer sheet. DARKEN CIRCLES COMPLETELY. Code your UFID number on your
answer sheet. 2 Print your name on this sheet and sign it also.
3 Do all scratch work anywhere on this exam that you like. Circle your answers on the test form. At the end of the
test, this exam printout is to be turned in. No credit will be given without both answer sheet and printout. (4) Blacken the circle of your intended answer completely, using a #2 pencil or blue or black ink. Do not
make any stray marks or some answers may be counted as incorrect. (5) The answers are rounded off. Choose the closest to exact. There is no penalty for guessing. If you
believe that no listed answer is correct, leave the form blank.
{6) Hand in the answer sheet separately. W 277?? 77777 1. When a certain rubber band is stretched a distance 3;, it exerts a restoring force F = on: + 5:132, Where a and b are
constants. The work done in stretching this rubber band from :r 2 0 to a: = L is: (1) .3132 /2 + bL3/3 (2) all + 251:2 (3) a + 2613 (4) 5L (5) at? + bLma 2. An object is constrained by a cord to move in a circular path of radius 0.5 m on a horizontal ﬁctionless surface. The
cord will break if its tension exceeds 16 N. The maximum kinetic energy the object can have is: (1) 4 J (2) 8 J (3) 16 J (4) 32 J (5) 64 J 3. An escalator is used to move 20 people (60 kg each) per minute from the ﬁrst
ﬂoor of a department store to the second floor, 5 m above. Neglecting friction,
the power required is approximately: (1) 1000 W (2) 100 W (3) 200 W (4) 2000 W (5) 50,000 W 4. For a block of mass m to slide without friction up the rise of height 11. shown,
it must have a minumurn initial speed of: (1) 1/5515 (2) 1/2x/317i (3) ugh/2 (4) 2W (5) 2x65 5. A small object of mass m starts from rest at the position shown and
slides aiong the frictionless loopthe—ioop track of radius R. What is the
smallest value of 1; such that the ojbject wilt slide without losing contact
with the track? (1) R/2 (2) R/4 (3) R (4) 2R (5) zero 6. The potential energy of a body of mass m is given by U z —mg:r + $4632. The corresponding force is: (1) mg — km (2) —mg$2/2 ~1~ 14:533/6 (3) mgx2/2 — isms/6 (4) —mg + ism/2 (5) —mg + For 7. Block A, with a mass of 4 kg, is stationary, while block B, with a mass of 8 kg, is moving at 3 m/s. The center of mass
of the two block system has a speed in m/s of: (1) 2 (2) 0 (3)1.5 (4) 3 (5) 12 8. A 500~kg sack of coal is dropped on a 2000kg railroad ﬂatcar which was initially @7500 kg
moving at 3 m/s as shown. After the sack rests on the ﬁatcar, the speed of
the ﬂatcar is: t 2000kg are
raw—w (1) 2.4 m/s (2) 0.6 m/s (3) 1.2 m/s (4) 1.8 m/s (5) 3.6 m/s Z7777 7777? 9. A cart loaded With sand slides along a horizontal frictionless track. As the car moves, sand trickles out at a constant
rate through a hole in the back of the cart. The speed of the cart Will: remain the same decrease at a constant rate
increase at a constant rate
decrease at a variable rate
increase at a variable rate 01%me 10. The angular speed in rad/s of the second hand of a watch is:
(1) 7T/30 (2) 7r/1800 (3) air/60 (4) 27: (5) 60 11. String is wrapped around the periphery of a 5.0—cm radius cylinder, free to rotate on its axis. If the string is pulled out
at a constant rate of 10 orn/s and does not slip out he cylinder, the angular velocity of the cylinder, in rad/s, is: (1) 2.0 (2) 5.0 (3) 10 B (4) 25 (5) 50 12. Four identical particles, each with mass m, are arranged in the ax, 3; plane as shown. They are connected by light sticks to form a rigid body. If m = 2.0 kg
and a z 1.0 m, the rotational inertia of this array about the y axis is: (1) 12 kg—m2
(2) 4.0 kgm2
(3) 9.6 kgm?‘
l4; 4.8 kgrn2
5 none of these 13. A sphere of radius R and mass M has a rotational inertia about a diameter that is given by gM/R? A string of length R is attached to the surface and
used to suspend the sphere from the ceiling. Its rotational inertia about the
point of attachment at the ceiling is given by X M R2 Where X is: 1 4.4 waww
9???
when 14. The coeﬂicient of static friction between a certain cylinder lying lengthwise and a horizontal ﬂoor is 0.40. If the rotational inertia of the cylinder about its symmetry axis is given by I : 2141432, then the maximum acceleration the cylinder can
have Without slipping is: (I) 089 (2) 029 (3) 049 (4) 01g (5) g a” 15. A thin—walled hollow tube rolls Without slipping along the ﬂoor. The ratio of its translational kinetic energy to its
rotational kinetic energy (about an axis through its center of mass) is: ' m1 @2 @3 m; m; 73777 77777 16. A hoop has a mass of 200 g and a radius of 25 cm. It rolls without slipping along level ground at 500 cm/s. Its total
kinetic energy, in J, is: g. :5 (1) 5 (2) 2.5 (3) 1o (4) 250 (5) need to be told the angular velocity
17. A ﬁ—kg particle moves to the right at 4 m/s as shown. Its anguiar momentum 4 m/s
in kgnzt2 /s2 about the point 0 is: 6 kg """"""""""" 30°
12 m (1) 144 (2) zero (3) 288 (4) 24 (5) 249 18. A ﬁrecracker is placed between two cans of mass m; and mg respectively, where m1 = 27712. Find the ratio of their
kinetic energies, E1 /E2, immediately after the ﬁrecracker explodes. (5) 2 OOH—1 (1) 3 (2) 1 (3) 1 (4) 19. A 0.1 kg ice cube (no friction), slides along a horizontal surface with velocity 6 m/s and hits a stationary ice cube of
mass 0.2 kg. The two stick together, then slide up a 30° siope to a height (measured vertically) of h. Find h. (1) 0.2 m (2) 0.1 In (3) 0.6 in (4) 0.3 In (5) 0.4 m 20. Two objects of mass m1 and m2 have the same kinetic energies. Find the ratio of their momenta, 101/102. (1) fme (2)m1/m2 (3) (ml/m2? (4) me/ml ('5) (me/mm O 2" 3
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