2nd LE Sample Exam(1)

Name: Section: Student Number: Course:Lecturer: College:

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University of the PhilippinesCollege of Science

PHYSICS 71SET A

2nd Semester AY 2010-2011

Second Long Examination

National Institute of Physics 2nd Semester AY 2010-2011 Physics 71

INSTRUCTIONS: Choose the best answer. Ignore air resistance, unless otherwise stated in a question. Acceleration due to gravity on the surface of the surface of the earth is 9.81 m/s2. Moment of inertia of some objects:

; ;

For the next THREE questions, consider the following: Gerold wants to bring a 15.-N box on top of a floor inclined at 300 with respect to the horizontal. To do this, he placed a massless pulley and used a massless string (see figure in the right) to pull the box.

1. Work I. Assuming the floor to be frictionless, what is the work done by Gerold if he moved the box 2.00 m along the incline while exerting a constant force of 10.0 N?

A. 0 J B. 10.0 JC. 15.0 J

D. 17.3 JE. 20.0 J

2. Work II. (Refer to previous question) What is the work done by gravity?

A. -30.0 JB. -26.0 JC. -15.0 J

D. 0E. 30.0 J

3. Work III. If the floor is not frictionless and the box is moving at constant velocity, which of the following force is doing the greatest amount of work on the box?A. FrictionB. Gravity C. Normal force

D. Force applied by Gerold E. Three of the forces above do

equal amount of work

4. Box has speed. A 20.0 kg box initially at rest has a net force of 30.0 N in the direction of its displacement. What is its speed after it moved 10.0 m?A. 3.87 m/sB. 5.48 m/sC. 10.0 m/s

D. 30.0 m/sE. 300. m/s

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National Institute of Physics 2nd Semester AY 2010-2011 Physics 71

5. Object objects. Which of the following statements is NOT ALWAYS TRUE for an object undergoing linear motion?A. The kinetic energy of an object cannot be negative.B. If there is no total work done on an object, then it is not accelerating.C. Work can be positive, negative, or zero but it has no direction in space.D. A higher positive total work done on an object with initial speed vo would

result to a higher speed than a lower positive total work.E. An object with a greater mass would require equal work to be moved the

same displacement as a lighter object using the same amount of force.

For the next TWO questions: Jessie pushes a 20.0-kg cabinet at a distance of 10.0 m starting at x = 0 along a horizontal frictionless floor by applying various amount of force, as shown in the right.

6. Jess I. What is the work done by Jessie on the cabinet upon moving it from x = 0 to x = 10 m?A. 24 JB. 32 JC. 40 J

D. 64 JE. 80 J

7. Jess II. What is the speed of the cabinet at x = 10.0 m if it started from rest?A. 1.5 m/sB. 1.8 m/sC. 2.0 m/s

D. 2.5 m/sE. 2.8 m/s

8. Oh K. A 5.00-kg mass slides along a frictionless horizontal ramp at an initial speed of 19.0 m/s and suddenly bumps into an ideal spring attached at the end of the ramp, causing the spring to be compressed a distance of 2.20 m before coming momentarily to rest. What is the spring constant?A. 43.2 N/mB. 44.6 N/mC. 49.1 N/m

D. 373 N/m E. 903 N/m

9. Motor Work. A certain elevator has a mass of 5.00 x 102 kg. With the maximum number of passengers inside, it ascends at a constant speed. The

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National Institute of Physics 2nd Semester AY 2010-2011 Physics 71

elevator is driven by a motor that can provide up to 3.00 x 104 W. What is the maximum work done by the motor if the elevator ascends a vertical distance of 15.0 m in 12.0 s?

A. 3.60 x 105 JB. 7.36 x 104 JC. 3.68 x 104 J

D. 4.91 x 103 JE. 2.50 x 103 J

10. June 21. You placed the 3.4 kg-Young and Freedman 12th edition book on top of a vertical spring with spring constant 300. N/m. What is the maximum compression of the spring?A. 0.011 mB. 0.11 mC. 0.22 m

D. 1.2 mE. 4.5 m

11. Starts with an S. Four projectiles, A, B, C and D, are thrown from the top of a 100-m tower with the same initial speed but different launching angles from the horizontal as shown in the figure. Which projectile landed to the ground with the greatest speed?A. Projectile AB. Projectile BC. Projectile CD. Projectile DE. The projectiles reach the ground with

the same speed.

12. Not velocity. Object Z is attached to a spring and moves in the trajectory as shown in the figure. The spring has an uncompressed and unstretched length of x0. At what time does the object have the greatest speed?A. t = 0 sB. t = 1 sC. t = 2 sD. t = 3 sE. It has the same speed for all

times

13. Loop the loop. A supertrain is traveling on a frictionless track as shown in the figure below. What is the minimum

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National Institute of Physics 2nd Semester AY 2010-2011 Physics 71

speed v of the supertrain at the lowest point for it to fully circle the circular loop of radius r?A. (gr)1/2 B. (3gr)1/2 C. 2(gr)1/2

D. (5gr)1/2

E. 3(gr)1/2

14. Conserve. Which of the following statements is/are ALWAYS true for conservative forces?

The work done, due to the force, on an object

I. is irreversible.

II. is path independent for all possible paths.

III. is zero if starting and ending points are the same.

IV. cannot be represented by a potential-energy function.A. I onlyB. II onlyC. I and IV only

D. II and III onlyE. II, III, and IV only

For the next TWO questions, refer to the figure at the right:

15. Potential Curve. How many equilibrium points are there in the plot? A. 1B. 2C. 3D. 4 E. 5

16. Force be with U. Of the following points, at which point is the force most positive?A. 1B. 2C. 4

D. 5E. 6

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17. Smiley. A uniform disk has its center of mass at pt. D as shown in (a). If a portion of the disk is removed as shown in (b), where is the new location of the center of mass?A. Above pt. DB. Below pt. DC. To the left of pt. DD. To the right of pt. DE. Still at pt. D

18. Impulse. Equal and constant forces of magnitude F are applied to object A (mass = m) and object B (mass = 2m) resulting to equal magnitudes of impulse J. The two objects are both initially at rest. Which is true about the magnitude of momenta and contact times of the applied forces of objects A and B? (pA and pB are momenta of A and B, respectively; ΔtA and ΔtB are contact times of A and B, respectively)A. pA = pB, ΔtA = ΔtB

B. pA = pB, ΔtA < ΔtB

C. pA = pB, ΔtA > ΔtB

D. pA < pB, ΔtA = ΔtB

E. pA > pB, ΔtA = ΔtB

19. J-P. An object has a net force, of magnitude F directed to the right, causing it to stop after some time interval. Which of the following is NOT TRUE about the motion of the object?A. The object has a non-zero initial momentum.B. The object has an initial momentum directed to the left.C. The object experienced an impulse directed to the left.D. The object experienced an impulse directed to the right.E. The object experienced an impulse of non-zero magnitude.

20. Jemi. Two objects with different masses collide and stick together. Before collision, the two-object system has_____________ compared to that after the collision.A. less total momentum and less total kinetic energyB. more total momentum but less total kinetic energyC. the same total momentum but less total kinetic energyD. the same total momentum but more total kinetic energyE. the same total momentum and the same total kinetic energy

21. What’s on the plate. A 0.0690-kg steel ball is released from rest and falls vertically from a height of 176 m onto an immovable, steel plate. The ball strikes the plate and is in contact with it for 1.00 x 10-3 s. The ball rebounds elastically, and returns to its original height. In this situation, the average force exerted on the ball during contact with the plate is___________.A. zeroB. 4.05 x 103 NC. 8.11 x 103 N

D. 1.62 x 104 NE. 4.05 x 105 N

22. Particles. A proton of mass m undergoes a head-on elastic collision with a stationary carbon nucleus of mass 12m. The speed of the proton is 300. m/s. The speed of the carbon nucleus after collision is________.A. zeroB. 25.0 m/sC. 46.2 m/s

D. 49.7 m/sE. 300. m/s

For the next TWO problems, consider the following: A sushi at the edge of a circular turntable, of radius 0.75 m, rotates with an angular displacement given by

= (1.0 rad/s2)t2 – (2.0 rad/s) t.23. Sushi I. What is the distance covered by the sushi from t=0.0 s to t=3.0 s?

A. 2.3 m B. 3.0 mC. 4.0 m

D. 4.5 mE. 6.0 m

24. Sushi II. At what time will the sushi’s angular velocity be equal to zero?

A. 1.0 s B. 3.0 sC. 5.0 s

D. 7.0 sE. 9.0 s

For the next TWO problems, consider the following: A gigantic flywheel of radius 6.0 m, initially at rest, begins rotating about its axis with a constant angular acceleration of 8.0 rad/s2.25. Dr. Manhattan I. How much time does it take for the flywheel to reach an

angular velocity of 52.0 rad/s?A. 24 s B. 12 sC. 6.5 s

D. 3.0 sE. 1.5 s

26. Dr. Manhattan II. How many revolutions does the flywheel turn in this time interval?A. 160 revolutionsB. 81 revolutionsC. 40. revolutions

D. 27 revolutionsE. 10. revolutions

27. Rank the Disks. Two different disks are attached to inextensible, massless strings [refer to the figure at the right]. Disk I has mass m and radius R. Disk II has mass 2m and radius 2R. After the disks are released from rest, they accelerate downward. Which of the following correctly describes the comparison of total kinetic energies of the disks after they traveled the same amount of displacement?

A.

B.

C.

D.

E.

28. Rank the Cylinders. Three cylinders I, II, and III have the same mass and same outer radius. The three cylinders were given the same amount of rotational kinetic energy and they are allowed to rotate about an axis parallel to their body passing through the axis of symmetry. Which of the following statements is true about the angular speed of the cylinders about their axis of rotation?

A.

B.

C.

D.

E.

29. Axis. Consider the homogeneous solid sphere at the right. Which of the following axis of rotations A, B, C, D and E will give the system the greatest moment of inertia?

30. Rolling down! A solid homogenous sphere (mass m = 1.0 kg; radius R = 0.25 m) is released from rest and rolls without slipping on a rough inclined plane from a height of 1.0 m. What is the speed of the sphere as it reached the bottom of the ramp? A. 2.6 m/sB. 4.4 m/sC. 3.7 m/s

D. 5.0 m/sE. 7.0 m/s

31. Torques. Two forces are applied on opposite ends of a 5.0-m long uniform rod, as shown in the figure. F1 = 5.5 N is applied perpendicular to the rod, while F2 = 8.0 N makes an angle of 40° from the horizontal. What is the net torque about the center of the rod due to these two forces? (The rod and the forces are in the plane of the page.)A. 0.89 Nm, into the page B. 0.89 Nm, out of the page C. 1.6 Nm, into the page D. 1.6 Nm, out of the page E. 27 Nm, into the page

For the next TWO questions, consider the following: A solid ball (M = 0.800 kg, R = 0.0300 m) rolls without slipping on a rough horizontal surface with a speed V0 = 1.75 m/s. It then encounters a rough ramp inclined at an angle of 45.0°. The coefficient of friction between the ramp and the ball is 0.300.

32. Ball I. What is the total kinetic energy of the ball at the bottom of the ramp?A. 0.490 JB. 0.980 JC. 1.23 J

D. 1.72 JE. 2.21 J

33. Ball II. At what height, from the bottom of the ramp, will the ball stop?A. 0.0624 mB. 0.125 mC. 0.157 m

D. 0.219 mE. 0.282 m

For the next TWO questions, refer to the following: A 4.2-m diameter merry-go-round is rotating freely with angular speed of 0.8 rad/s. Its total moment of inertia is 1260 kg m2.

34. MERRY I. What is the angular momentum of the merry-go-round?A. 5 x 102 kg∙m2/s B. 8 x 102 kg∙m2/sC. 1 x 103 kg∙m2/s

D. 2 x 103 kg∙m2/sE. 1 x 106 kg∙m2/s

35. MERRY II. How much work will bring the merry-go-round to rest?A. -0.9 JB. -400 JC. -500 J

D. -800 JE. -1000 J

36. STICK. A thin uniform stick of mass M = 0.30 kg and length d = 1.50 m is attached to a pivot at the top. A piece of clay of mass m = 1.0 kg and speed v = 1.2 m/s hits the stick a distance x = 0.70 m from the pivot and sticks to it. Find the angular speed of the stick just after the clay sticks to it.A. 0.91 rad/sB. 1.0 rad/sC. 1.2 rad/sD. 1.6 rad/sE. 2.0 rad/s

37. SKATER. A figure skater standing on a frictionless icy surface spins around with her arms extended. When she pulls in her arms, her angular speed increases so that her angular momentum is conserved. Compared to her initial rotational kinetic energy, her rotational kinetic energy after she has pulled in her arms must be ____________.A. the sameB. larger because she is rotating fasterC. larger because her rotational inertia is larger

D. smaller because her rotational inertia is smallerE. smaller because energy was dissipated during her spin

38. Ramp up. Consider a box, of mass m = 1 kg, sliding on a frictionless floor. It is moving towards a rough ramp at a constant speed of 5 m/s. The ramp is 0.5 m tall, 1.58 m long, and has a coefficient of kinetic friction μk = 0.1. What will the ball's final speed be as it reaches the top of the ramp?A. 6.13 m/sB. 5.64 m/sC. 5.27 m/sD. 3.50 m/sE. 2.47 m/s

For the next TWO questions, consider the following: A pulley system used to lower a big box consists of a light rope wrapped around a solid disk with a radius of 3.00 m and a mass M = 11.0 kg. As the box falls, the rope unwinds without stretching or slipping, turning the disk. The maximum angular acceleration of the hoop is 2.50 rad/s2.39. PULLEY I. What is the magnitude of the tension along the

rope to maintain the maximum angular acceleration of the hoop?A. 41.3 NB. 82.5 NC. 124 N

D. 248 NE. 495 N

40. PULLEY II. What is the largest mass of the box that the pulley system can carry for the rope to unwind without slipping?A. 2.39 kgB. 17.9 kgC. 35.7 kg

D. 53.7 kgE. 107 kg

41. Parallel Axis Theorem. The center of mass of the slender rod (of total length L and linear density ρ = kx) is located from the left end of it (refer to the figure). The moment of inertia about an axis at the left end perpendicular to

the rod is , where m is the total mass of the rod. What is the

moment of inertia, about an axis at the right end of the rod perpendicular to

it?

A.

B.

C.

D.

E.

42. Ballistic Pendulum. A high-school pitcher is employing a ballistic pendulum to determine the speed of his fastball. A 4.0 kg lump of clay is suspended from a taut cord 2.0-m long. When the pitcher throws his fastball aimed at the clay, the ball becomes embedded in the clay and the two swing up to a maximum height of 0.10 m. If the mass of the baseball is 0.20 kg, the speed of the pitch is_____.A. 1.5 m/sB. 6.4 m/sC. 7.1 m/sD. 29 m/sE. 31 m/s

END OF EXAM