physics712ndle1stsem20112012

University of the PhilippinesCollege of Science

Physics 71

Set ASecond Long Exam

First Semester AY 2011-2012

Name: Instructor:

Section/Class Schedule: Student Number:

Course: College

Physics 71/Second Long Exam A Page 2 of 12 1st Sem AY 2011-2012

Instructions: Choose the letter of the best answer. Ignore air resistanceunless stated otherwise. The acceleration due to gravity is: g = 9.81

[ms2

].

1. Push it. Leslie pushes a 10.0 [kg] cabinet horizontally on a level surface with anapplied force of 25.0 [N]. If the cabinet slides on the surface by 5.00 [m], what isthe work done by gravity on the cabinet?

(a) 491 [J] (b) 125 [J] (c) -491 [J] (d) - 125 [J] (e) 0

2. Cable. A 10. [kg] object is hoisted by a cable whose tension is 140[N]. What isthe total work done on the object as it moves 2.0[m]upward?

(a) 42 [J] (b) 84 [J] (c) 130 [J] (d) 260 [J] (e) 280 [J]

3. Crash Collision. Two cars were moving in a collision course with each other, butSuperman prevented the collision by stopping both cars with his hands. Car A hasa mass of 2000 [kg] and was moving with a speed of 200

[kmh

]. Car B, which has a

mass of 4000 [kg] , was approaching car A from the opposite direction with a speedof 150

[kmh

]. To which car did Superman do greater work?

(a) car A

(b) car B

(c) Equal amount of work will be done toboth cars.

4. Falling. Romeo dropped a 0.0150 [kg] ring from rest at a 22.0-m high building.Juliet, who is directly below the falling ring, placed her hands on the ground. Whatis the speed of the ring just before it reaches Juliets hands?

(a) 0 (b) 14.7[ms

](c) 20.8

[ms

](d) 216

[ms

](e) 432

[ms

]


5. Area under the curve. A force F is applied toa box of mass 2.0 [kg] parallel to the x-axis as itmoves along a straight line. The x - componentof the force varies with the x - coordinates ofthe box as shown below, with the force given inNewtons and the position in meters. What isthe work done on the box by F as it moves fromx = 1.0 to x = 5.0?

(a) 0 [J] (b) 4.0 [J] (c) 10. [J] (d) 20. [J] (e) 25. [J]

6. Moving particle. A particle experiences aforce, which acts along the x-axis, as describedin the force vs. position plot shown. What isthe work done by this force if it starts at x=2.0m and ends at position x=0?

(a) 0 J

(b)0.5 J

(c) 1.0 J

(d) -0.5 J

(e) -1.0 J

7. K+U. You throw a rock straight up with initial speed v from the ground. Whichof the following graphs can represent the rocks mechanical energy, E, as a functionof time while the rock is in air?


8. K-U. At time t = 0, you throw a rock straight up with initial speed v fromthe ground. Let K and U be the kinetic and potential energies of the particle,respectively, and let U=0 when the rock is on the ground. Which of the followinggraphs show the quantity K U as a function of time?

9. Pellet Gun. A 0.10-kg pellet is launched straight up from a pellet gun, whichcontains a spring of spring constant k = 5.0 102 [Nm]. Right before launching,the spring is compressed a distance 0.050 m, and the pellet is at rest. From thisinitial position, the pellet is observed to reach its maximum height at 0.40 m aboveits starting point. Find the work done by air resistance as the pellet goes from itsstarting point to its maximum height.

(a) -0.23 [J] (b) -1.0 [J] (c) 0 [J] (d)0.23 [J] (e) 1.0 [J]

10. Glider. A 0.45 [kg] glider that sits on a frictionless air track is connected to aspring with spring constant 2.5 [N/m]. Initially, the spring is unstretched so thatthe glider is in equilibrium. Patty then stretches the glider by a distance of 0.25[m]. What is the work done by the spring on the glider?

(a) -0.16 [J] (b)0.16 [J] (c) -0.078 [J] (d) 0.078 [J] (e) 0

11. Conservative. If the only forces that do work on a system are conservative, whichof the following quantities must remain constant?

(a) Kinetic Energy

(b)Gravitational Potential Energy

(c) Elastic Potential Energy

(d) Total Mechanical Energy


12. Cellphone. Jones cellphone with mass of 0.150 [kg] is placed on top of a table.Ana slid the cellphone to the right by a distance of 3.00 [m]. After seeing this, Joneimmediately returned the cellphone back to its initial position by sliding it to theleft by a distance of 3.00 [m]. If the coefficient of kinetic friction between the tableand the cellphone is 0.0100, what is the total work done by kinetic friction on thecellphone?

(a) 0 (b) 0.0441 [J] (c) 0.0883 [J] (d) -0.0441 [J] (e) -0.0883 [J]

13. Energy diagram. How many stableand unstable equilibrium points can youfind in the figure?

(a) 0 stable equilibrium points, 1 unsta-ble equilibrium point

(b)1 stable equilibrium point, 0 unstableequilibrium points

(c) 0 stable equilibrium points, 0 unsta-ble equilibrium points

(d)2 stable equilibrium points, 1 unsta-ble equilibrium point

(e) 1 stable equilibrium point, 2 unstableequilibrium points

14. Axes. You throw a ball from theground at an angle above the horizon-tal such that it follows the trajectory asshown at the right. Which of the follow-ing statements correctly describes theball at the peak of its trajectory, pointP?

(a) It is in stable equilibrium.

(b) It is in unstable equilibrium.

(c) It is in neutral equilibrium.

(d) It is not in equilibrium.

15. Thanks to Dobby. Remember that Harry was once unable to get to Platform 9and 3/4. If Harry weighed 491[N] then, and he was running towards the barrier at1.0[ms

], what is the magnitude of the average force that the barrier must exert on

him such that the contact time is just 0.010 [s]and he rebounds at 3.5[ms

]?


(a) 2.3104[N] (b) 1.3104[N] (c) 2.2103[N] (d) 4.0 [N] (e) 1.3 [N]

16. Impulse. The speed of a pitched baseball of mass 0.10 [kg] is 90.[ms

]. Right after

the ball is batted, it moves with a speed of 100.[ms

]in the direction opposite to its

original velocity. What is the magnitude of the impulse of the net force on the ballduring the collision?

(a) 1.0 [N s] (b) 10 [N s] (c) 19 [N s] (d) 190 [N s] (e) 19,000[N s]

17. Conservation of Momentum. Which of the following statements regarding thelaw of conservation of momentum is FALSE?

(a) It is valid only when internal forces in the system are conservative

(b) It is valid even when internal forces in the system are non-conservative

(c) It is valid only in inertial frames of reference

(d) It is valid if vector sum of external forces is zero

(e) It is valid if total rate of change of momentum of the entire system is zero

18. Skaters. In a figure skating competition, an 80.0-kg boy and a 60.0-kg girl collideand grab on to each other on very smooth ice so that both move with the samevelocity afterwards. Before the collision, the boy was moving to the right at 1.80[ms

], while the girl was moving to the left at 2.50

[ms

]. What is their velocity just

after the collision?

(a) 4.29 102 [m/s] to the left(b) 4.29 102 [m/s] to the right(c) 2.1 [m/s] to the left

(d) 2.1 [m/s] to the right

(e) 0

19. Gunman. A gunman holds a rifle tightly against his shoulder and fires the riflehorizontally using a 5.00 [g] bullet with an initial velocity of 350 [m/s]. The com-bined mass of the gunman and the rifle is 115 [kg] . What is the recoil velocity ofthe gunman with the rifle?

(a)1.52 102 [ms ](b)+1.52 102 [ms ] (c)1.64 10

2 [ms

](d) +1.64 102 [ms ]


20. Ballistic Pendulum. A 5.00-[kg] boxis suspended from the ceiling by a cordthat is 50.0 [cm] long. A 10.0-[g] bul-let was fired horizontally with speed at350 [m/s] into the box. By how muchwill the vertical height of the pendulumchange?

(a) 2.48 [cm] (b)2.56 [cm] (c) 3.12 [cm] (d)3.98 [cm] (e) 4.21 [cm]

21. Standard collision. An object B of mass 2.0[kg]moving at 5.0[ms

]to the left

strikes a stationary object A. A completely inelastic collision occurs and the com-posite object moves at 2.0

[ms

]to the left. What is the mass of object A?

(a) 1.0[kg] (b) 2.0[kg] (c) 3.0[kg] (d)4.0[kg] (e) 5.0[kg]

22. Elastic Collision. A 1.00-[kg] block is moving on a frictionless, horizontal airtrack with a speed of 0.800

[ms

]to the right. It makes a collision with another

glider that has a mass of 0.800-[kg] that is moving to the left with a speed of 2.50[ms

]. What is the final velocity of the 0.800-[kg] glider after the elastic collision?

(a) 1.17[ms

]to the right

(b)1.17[ms

]to the left

(c) 2.14[ms

]to the right

(d) 2.14[ms

]to the left

(e) 3.30[ms

]to the right

23. Vectors. A point mass m is revolving withuniform speed in the clockwise direction alongthe circular path of radius R. The center ofthe circle coincides with the origin of the three-dimensional rectangular coordinate system. Atthe instant shown in the figure, what is the cor-rect order of the directions for the following vec-tor quantities: net force on the mass, in-stantaneous velocity, and angular velocityof the mass?

(a) Net force is zero; j; j

(b)Net force is zero; j; k(c) i; j; j

(d) i; j; k

(e) i; j; k


24. Constant speed. Anna and Bob are on a merry-go-round of radius R whichrotates with constant angular speed. Anna is standing a distance R/2 from thecenter, while Bob is standing a distance 3R/4 from the center. Which of thefollowing statements is/are TRUE?

I. Bob and Anna have the same acceleration.

II. Bob and Anna have the same linear speed.

III. Bob and Anna have the same angular acceleration.

(a) I only (b) II only (c) III only (d) I and II only (e) I and III only

25. Circular Motion A body moving in a circular path has constant angular accel-eration of 1.0

[rads2

]. If its initial angular velocity is 5.0

[rads

], what is its angular

velocity after 2.0 [s]?

(a) 9.0[rads

](b) 7.0

[rads

](c) 2.0

[rads

](d) 3.0

[rads

](e) 1.0

[rads

]26. Revolution.

A rotating disk experiencing uniform angular acceleration starts from rest toan angular speed of 3.14 rad/s in 30.0 s. What is the magnitude of the angularacceleration of the disk?

(a) 0.100[rads2

](b)0.105

[rads2

](c) 0.314

[rads2

](d)30.0

[rads2

](e) 94.2

[rads2

]27. Weight training. For the same total mass M of each given object, which has

the greatest rotational kinetic energy if they both rotate with the same angularvelocity about an axis perpendicular to its shaft?

(a) A barbell with mass M concentrated near the ends of its 1.0-meter length rotat-ing about the middle of its shaft.

(b)A dumbbell with mass M concentrated near the ends of its 1.0-ft length rotatingabout the middle of its shaft.

28. Rotational Motion. A solid sphere, a ring and a spherical shell of the samemasses and radii are made to roll without slipping along an incline with the sameinitial velocity v0 and the same initial height. Which of the following quantitiesare equal for all objects at the moment that each object reaches the bottom of theincline?

(a) Translational kinetic energy

(b)Rotational kinetic energy

(c) Total kinetic energy

(d)Time of descent


29. Solid cylinder. What is the moment of iner-tia of a uniform solid cylinder with a radius of1.5[m]and mass 3.0[kg]about an axis along theedge of the cylinder and running parallel to itslength?

(a) 6.8[kg m2]

(b)10.[kg m2]

(c) 14.[kg m2]

(d) 20.[kg m2]

(e) 41[kg m2]

30. Parallel axis theorem.When a net external torque of magnitude 64.0 [N m] is applied to a long uniform

rod of mass 10.0 kg, it will rotate about its center of mass with angular accelerationof magnitude 1.57

[rads2

]. If a torque of the same magnitude is applied to the

same rod about a parallel axis 1.00m away from the original axis, what is the newmagnitude of the angular acceleration?

(a) 1.26[rads2

](b)1.57

[rads2

](c) 11.6

[rads2

](d) 50.8

[rads2

](e) 74.0

[rads2

]31. Torque. Object B moves with constant speed in a cir-

cular path with radius R. It is acted upon by a singleforce Fa. What is the magnitude of the torque about thecenter of the circular path?

(a)RFa.

(b) zero

(c) Cannot be obtained because the speed of the objectis not given.

32. Seesaw. A 50.0-[kg] girl and a 60.0-[kg]boy sit on the opposite sides of a seesaw,each child a distance of 2.00[m]fromthe fulcrum. The boy sits on the sidethat is initially higher, so that the see-saw swings about the fulcrum. At themoment when the seesaw is horizontal,what is the net torque on the seesaw?

(a) 20.0 [N m]into the page(b)20.0 [N m]out of the page(c) 10.0 [N m]into the page


(d)10.0 [N m]out of the page(e) The net torque is zero since the seesaw is horizontal.

33. Sleeping Beauty. Aurora is trying to spin thread on a wheel. She applies a forcetangent to the wheel, giving it a torque of 2.0 [N m]. If the wheel has a momentof inertia equal to 1.0

[kg m2], what is the wheels angular acceleration?

(a) 0.50[rads2

](b) 0.50

[revs2

](c) 1.0

[rads2

](d) 2.0

[revs2

](e) 2.0

[rads2

]34. Angular dynamics. A disk of radius

0.120[m]and moment of inertia 1.44104 [kg m2]is initially spinning with uniform angular speedof 21.0

[rads

]about a fixed axis perpendicular to

its plane and passing through its center. Youtried to stop it by applying a force of magnitude0.100 [N]perpendicular to the thickness of thedisk, as shown in the figure. If the coefficient ofkinetic friction between your hand and the disk surface is 0.200, how long will ittake before the disk comes to a full stop?

(a) 2.40 103 s(b)1.20 102 s(c) 0.252 s

(d) 1.26 s

(e) 16.7 s

35. Keep em rollin. The same amount of work is done on three identical disks, R,S, and T , all of which are initially at rest. R slides on top of a frictionless surface,S rotates about its stationary center of mass, and T rolls without slipping. Whichdisk gained the highest total kinetic energy?

(a)R

(b)S

(c) T

(d)R and T

(e) All have the same total kinetic energy.

36. Rolling Cylinder. A solid cylinder starts from rest and rolls without slippingdown a hill. After its center of mass drops a total vertical distance of 2.0[m], whatis the speed of the center of mass of the cylinder?

(a) 3.1[ms

](b)3.8

[ms

](c) 4.4

[ms

](d) 5.1

[ms

](e) 6.3

[ms

]


37. Weaker. A torque resulted in an angular speed with power P. If the torqueis doubled, how much power will be measured when the resulting angular speed ishalf of the original value?

(a) P/4 (b) P/2 (c) P (d)2P (e) 4P

38. Energy DVD. Consider two very thin discs A and B. Disc A has twice the radiusand half the mass of disc B. Each disc, initially at rest, is made to rotate about anaxis through its center of mass perpendicular to the plane of the disc. Which discrequires greater energy in order to complete 1 revolution after 1 second?

(a) Disc A

(b)Disc B

(c) Both require the same amount ofpower

39. Angular momentum. A thin uniform rod of mass 1.12 [kg] and length 0.750[m]that is initially at rest is pivoted at its center of mass. A constant net torqueof magnitude 4.20 [N m]is applied to the rod. After 2.00 [s], what is the angularmomentum of the rod?

(a) 0.0525[kgm2

s

](b)8.40

[kgm2

s

](c) 80.0

[kgm2

s

](d) 160.

[kgm2

s

](e) 212

[kgm2

s

]

40. Collide. Two discs A and B, with moments of inertia Ia and Ib respectively, areattached to a horizontal rod through their centers of mass. A is rotating at anangular speed a while B is at rest. If we bring the two discs together by applyinga force very near the axis (thereby applying negligible torque), what will be theresulting angular speed of the two discs?

(a) = Iaa/(Ia + Ib)

(b) = Iaa/(Ia Ib)(c) = Iba/(Ia + Ib)

(d) = Iba/(Ia Ib)

41. Conservative and nonconservative.A small box of mass 1.20 [kg] starts fromrest at a height 4.25 [m]on top of a rampinclined at 60 with respect to the hor-izontal. Upon release, the box slidesdown to a level surface of length 3.50[m]before ascending again at anotherramp inclined at 45 with respect to thehorizontal. If all surfaces have constant coefficient of kinetic friction = 0.250,what is the maximum height h that the box can reach in the other incline?

(a) 1.11 [m] (b) 2.21 [m] (c) 2.91 [m] (d)3.50 [m] (e) 4.25 [m]


42. Loop-the-loop. A stunt man rides asled through a loop-the-loop track of ra-dius R. He is initially at a height habove the ground, as shown in the fig-ure. Assuming that the track is friction-less, what is the minimum value of theheight h for the stunt man to go through the loop-the-loop safely?

(a)R/2 (b)R (c) 3R/2 (d)2R (e) 5R/2

End of Second Long Exam

physics712ndle1stsem20112012

Documents

isthe work

position x

greater work

force f

isthe total work

pellet gun

anapplied force

car ab car bc equal