physics 71 1st long exam

University of the Philippines College of Science

PHYSICS 71

SET A

2nd Semester AY 2010-2011

First Long Examination

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

A-2

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.

1. HINDI TAMAD. As an exercise every morning, Juan walks to his favorite bakery, five kilometers away from his house. On the way back to his house,

he always sprints. Which of the following statements is ALWAYS TRUE?

A. Juan’s average speed for the whole trip is zero. B. Juan’s average speed for the whole trip is equal to the magnitude of his

average velocity.

C. The magnitude of Juan’s displacement for the whole trip is greater than the distance he traveled.

D. The magnitude of Juan’s displacement for the whole trip is equal to the dis

tance he traveled.

E. The magnitude of Juan’s displacement for the whole trip is less than the distance he traveled.

2. KINEMATICS. Which of the following is NOT possible?

A. An object has velocity directed east and acceleration directed west.

B. An object has velocity directed east and acceleration directed east.

C. An object has zero velocity but non-zero acceleration.

D. An object has constant non-zero acceleration and changing velocity.

E. An object has constant non-zero velocity and changing acceleration.

3. X vs. t. Shown below is a graph of an object’s position as a function of time.

Which of the following statements best describes the object’s motion? (Assume the forward direction to be the positive direction.)

A. The object rolls along a flat surface,

then rolls forward down a hill and

stops.

B. The object is initially not moving. It

then rolls forward down a hill and

stops.

C. The object is moving at a constant

velocity. It then slows down and stops.

D. The object is initially not moving. It

then moves backward and stops.

E. The object moves along a flat area,

and then moves backward down a hill.


A-3

For the next two questions: A particle moves along a straight path. Its position

as a function of time is described by the following graph:

4. PLOT I. What is the particle’s average velocity for the entire motion? A. Zero

B. -0.033 m/s

C. -0.083 m/s

D. 0.033 m/s

E. 0.083 m/s

5. PLOT II. At which time/s does the particle have the highest magnitude of instantaneous velocity?

I. At t = 15 s II. At t = 25 s III. At t = 45 s

A. I only

B. II only

C. III only

D. I and II

E. I and III

6. SKID MARKS. While braking, a car leaves 92.0-meter long skid marks on the

highway before coming to a stop. Assuming it slows down at a rate of 7.00

m/s2, what is the speed of the car just before braking? A. 25.4 m/s

B. 35.9 m/s

C. 42.5 m/s

D. 1290 m/s

E. 1810 m/s

7. STOPPING DISTANCE. A car slows down uniformly from a speed of 21.0 m/s

to rest in a time interval of 6.00 s. How far did it travel in that time interval? A. 63.0 m

B. 189 m

C. 116 m

D. 137 m

E. 126 m

8. CATCH. A ball player throws a ball vertically upward. He catches the ball

3.00s later on the same level as he threw it. With what speed did he throw it?

A. 3.80 m/s B. 9.00 m/s

C. 14.7 m/s

D. 29.4 m/s E. 44.1 m/s


A-4

9. IN FREE FALL. Which of the following statements is TRUE about an object in

free fall?

A. Its acceleration and velocity always have the same direction.

B. An object thrown upward has zero acceleration at the highest point.

C. At a given location near the surface of the Earth and in the absence of air

resistance, all objects fall with approximately constant acceleration.

D. An object thrown vertically upward will return to its original position with

different speed due to acceleration due to gravity.

E. As a freely falling object speeds up, its acceleration decreases in

magnitude.

10. ACCELERATION. An object is moving at velocity: v = 1.0 m/s î - 1.0 m/s ĵ at all times. Which of the following choices can be the object’s acceleration?

A. B. C. D. E.

For the next two questions: The figure below shows the trajectory of an ant as

it moved from point A to point B. The ant’s trip lasted for 10.0 s.

11. VAVE. What is the magnitude of the ant’s average velocity for the whole trip? A. 0.00 m/s

B. 0.20 m/s

C. 0.40 m/s

D. 0.90 m/s

E. 0.94 m/s

12. SAVE. What is the ant’s average speed for the whole trip?

A. 0.00 m/s

B. 0.20 m/s C. 0.40 m/s

D. 0.90 m/s

E. 0.94 m/s


A-5

13. PROJECTILE. Which of the following is ALWAYS FALSE about projectile

motion? A. The velocity is zero at the maximum height.

B. The horizontal component of velocity is constant all throughout the

motion. C. The horizontal and vertical components of projectile motion can be solved

independently.

D. The velocity along the vertical changes direction after it passes the maximum height.

E. The time it takes to reach the maximum height from a certain initial level

is equal to the time it takes to return to its initial level from the maximum height.

For the next three questions: A tennis ball on the ground is located 3.45

meters from a 1.00-meter high net. It is then hit at an angle of 30.0° above the

horizontal, such that the ball is at its maximum height when it is just above the net.

14. TENNIS I. What is the vertical component of the ball’s initial velocity?

A. 4.11 m/s B. 4.43 m/s

C. 5.42 m/s

D. 7.67 m/s E. 8.86 m/s

15. TENNIS II. What is the horizontal component of the ball’s velocity when it’s above the net?

A. 4.11 m/s

B. 4.43 m/s C. 5.42 m/s

D. 7.67 m/s

E. 8.86 m/s

16. TENNIS III. What is the total time that the tennis ball is in the air?

A. 0.32 s B. 0.45 s

C. 0.64 s

D. 0.90 s E. 1.10 s

17. CIRCULAR ROAD. What is the magnitude of the acceleration of a car

travelling with a constant speed of 5.0 m/s along a circular road with 10.0 m radius?

A. 0.40 m/s2

B. 0.50 m/s2 C. 1.00 m/s2

D. 2.00 m/s2

E. 2.50 m/s2


A-6

18. TOY CAR. A toy car runs around a circular track of radius R with speed equal

to v and centripetal acceleration magnitude a. Which of the following combination of speed and radius would result to a centripetal acceleration with

magnitude 4a?

A. v and R B. v and 2R

C. 2v and 2R

D. 2v and R E. ½v and R

19. MOTION VECTORS. Object A moves around a circular path with a constant

speed. Object B moves around the same circular path with varying speed.

Both move in clockwise direction. Which statement/s is/are ALWAYS TRUE when the objects pass through the same point on the path?

I. The acceleration of the objects point in the same direction.

II. The velocity of the objects point in the same direction.

III. The displacement of the objects point in the same direction. A. I only

B. II only

C. III only

D. I and II

E. II and III

20. RIVER. A river is flowing at 1.00 m/s due north. If a man drove his motorboat

2.00 m/s 45.00 north of west relative to the river, what is the boat's velocity

relative an observer standing on the banks? A. 1.47 m/s due north

B. 1.47 m/s 160 west of north

C. 1.47 m/s 160 north of west D. 2.80 m/s 600 west of north

E. 2.80 m/s 600 north of west

21. REFERENCE FRAME. Which of the following is an inertial reference frame? A. Inside a car rounding a curve at constant speed

B. Inside a car speeding up in a downward slope

C. Inside a car slowing down up an upward slope

D. Inside a car falling off a cliff E. Inside a sinking ship at constant velocity

22. SECOND. Which is TRUE about Newton’s second law? A. It states that if a net internal force acts on a body, the body accelerates

with direction same as the direction of the net force.

B. It states that a body acted on by a non-zero net force moves with constant velocity and zero acceleration.

C. It is valid in all frames of reference.

D. It is valid only in inertial frames of reference. E. It is a restatement of the law of action and reaction.


A-7

For the next two questions: A rectangular box attached to a

massless string is held stationary and in contact with a rough wall as shown in the figure on the right.

23. CONTACT. How many contact force/s is/are acting on the box?

A. 0 B. 1

C. 2

D. 3 E. 4

24. FORCES. Which of the following forces is/are exerted by the wall on the box?

I. Friction

II. Tension III. Normal force

A. I only

B. II only

C. III only

D. I and II

E. I and III

25. MR. MONKEY I. If an astronaut named Mr. Monkey has a mass of 35.0 kg on

planet X with a gravitational acceleration’s magnitude that is half of Earth’s. What would be the magnitude of his weight on planet Earth?

A. 1.75 x 101 N

B. 1.72 x 101 N C. 1.72 x 102 N

D. 3.43 x 101 N

E. 3.43 x 102 N

26. MR. MONKEY II. On Earth, Mr. Monkey throws a bunch of bananas, weighing 12.1 N, with a horizontal force of 15.0 N. At the moment it was thrown, what

is the horizontal acceleration of the bananas?

A. 1.24 m/s2 B. 1.53 m/s2

C. 2.35 m/s2

D. 9.81 m/s2 E. 12.2 m/s2

27. PARTICLE X. A newly discovered particle, with mass equal to 1.23x10-4 kg, is

given a force of ji ˆ)6

100.15(ˆ)6

100.13( NxNx . What is its acceleration?

A. ji ˆ)2

/5

1050.1(ˆ)2

/5

1030.1( smxsmx

B. ji ˆ)2

/7

1050.1(ˆ)2

/7

1030.1( smxsmx

C. ji ˆ)2

/7

1022.1(ˆ)2

/7

1006.1( smxsmx

D. ji ˆ)2

/10

1022.1(ˆ)2

/10

1006.1( smxsmx

E. ji ˆ)2

/1022.1(ˆ)2

/1006.1(1111

smxsmx


A-8

28. SQUISH. A particle with a mass of 1.0 kg is acted on by three different forces

of same magnitude equal to 10. N as shown. The particle is located where the tips of the arrows meet and the arrows represent vector forces. What is the

resultant acceleration of the particle?

A. (

) (

)

B. (

) (

)

C. (

) (

)

D. (

) (

)

E. (

) (

)

29. REACTION. A passenger of weight W rides in an elevator. The reaction force

to the weight of the passenger is A. the force of the earth on the floor.

B. the force of the floor on the passenger.

C. the force of the passenger on the floor.

D. the force of the earth on the passenger. E. the force of the passenger on the earth.

30. FBD. A piano is sitting on a rough horizontal floor. Chiaki pushes on the piano with a force FA that makes an angle θ from the horizontal, and the piano

slides along the floor. Which is a possible free body diagram of the piano?

(FN = normal force; FG = weight, Ff = friction)

A. B. C. D. E.


A-9

Ff

FN

Fg

FA

31. RIDER CHANGE! Robert Akizuki

attempts to jump across a deep ravine with his motorcycle as shown in the

figure. He accelerates towards the end

of the first cliff and jumps off it at an angle θ from the horizontal. What is the

free body diagram of the Robert-

Motorcycle system at the peak of its trajectory?

(N = normal force exerted by the 1st

cliff, W = total weight of Robert and motorcycle)

A. B. C. D. E.

32. FBD ULIT. The figure depicts a free body diagram of an object moving along

a horizontal surface. The arrows in the figure have the same lengths. Which of the following statements is TRUE?

A. The object is accelerating.

B. The object is moving at constant velocity. C. The object is moving towards the right with increasing

speed.

D. The object is moving towards the right with decreasing speed.

E. The object is moving towards the left with increasing

speed.

33. FORCE THAT PENETRATES. Boxes A, B, C, and D have the same mass of 4.0

kg. The boxes are lying on a frictionless horizontal floor, as shown in the figure

below. A force with magnitude of 32 N is applied on the left of box A which causes the boxes to accelerate at 2.0 m/s2. What is the magnitude of the force

exerted by box B on box C?

A. Zero B. 8.0 N

C. 16 N

D. 24 N E. 32 N


A-10

34. CHAI. Chai weighs 560. N in an inertial system. She stood on a weighing scale

inside an elevator that is accelerating 3.00 m/s2 upward. She noticed that the weighing scale registers a different weight. What is the mass of Chai inside the

accelerating elevator?

A. 17.0 kg B. 40.0 kg

C. 57.0 kg

D. 74.0 kg E. 187 kg

35. TENSION. Each of the blocks hanging on the left

side of the pulley system has a weight of 5.0 N. The

block hanging on the right side weighs 10. N. What is the magnitude of the tension at point A?

A. zero

B. 5.0 N

C. 10. N D. 15 N

E. 20. N

36. KINETIC. Jessie is pushing an 80-kg box along a horizontal rough surface.

He caused the box to move with a horizontal force of 350N. To maintain a

constant speed, he continuously applies a 200 N force. What is the surface’s

coefficient of kinetic friction?

A. 0.23

B. 0.25

C. 0.40

D. 0.45

E. 0.70

37. BANKED. Two identical cars, Car A and Car B, are making their turn on

banked curves, Curve A and Curve B, respectively. Curve A is banked with an angle θA and has a radius of the curvature RA, while curve B is banked with an

angle θB and has a radius of the curvature RB. What is the ratio of the speed of

car A over the speed of Car B if both cars need no frictional force to make their turn?

A.

B

A

BR

AR

Bv

Av

tan

tan

B.

B

A

AR

BR

Bv

Av

tan

tan

C.

A

B

BR

AR

Bv

Av

tan

tan

D.

A

B

AR

BR

Bv

Av

tan

tan

E. 1

Bv

Av


A-11

For the next two questions: A pail of water is swung in a

vertical circle with a radius r, as shown in the figure at the right. The mass of the water is m.

38. PAIL I. What is the magnitude of the force exerted on the water by the pail at

the top of the circle?

A.

g

r

vm

2

B.

g

r

vm

2

C. r

vm

2

D. mg

E. zero

39. PAIL II. What is the minimum speed needed for the water to remain in the

pail?

A. rg

B. m

rg

C. rg

D. 2

rg

E. Zero

40. DARNA. Narda drops a stone from rest at a

height h above the top of the window. From the

top of the window, it takes 0.28 s to reach the bottom of the window. If the height of the

window is 2.2 m, what is the height h?

A. 0.33 m B. 0.47 m

C. 2.14 m

D. 4.34 m E. 8.30 m

h

2.2 m


A-12

41. AAVE. The motion of an object can be determined at all times by the following

function of its position [r(t)], velocity [v(t)] and acceleration [a(t)]:

*(

) + *(

) +

*(

) + *(

) +

*(

) + *(

)+

What is the magnitude of the average acceleration in the interval t=0.0s to t=2.0s?

A. 10. m/s2

B. 19 m/s2

C. 25 m/s2 D. 38 m/s2

E. 49 m/s2

42. SLED. Ella with mass M sits on a sled (mass m) that rests on an icy surface

which can be assumed to be frictionless. Anton tied a rope in the sled and

pulled it with a horizontal force F. The coefficients of static and kinetic friction

between Ella and the sled are s and k , respectively. What is the maximum

magnitude of F such that Ella will not slide relative to the sled?

A. gmM s)(

B. gmM s)(

C. gmM k)(

D. sMg

E. smg

END OF EXAM

physics 71 1st long exam

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