Download TEST 2 (96-97) Laws of Motion/5-7

AP Physics 1 Test Review
Name
UNITS 5-7: Mass, Weight, and the Laws of Motion
The upcoming test will cover all material from investigations five through seven. Test topics thus include
weight, mass, inertia, and all applications of the three laws of motion. Traditionally, this test has proved to
be difficult because of the many possible problems that involve the application of the laws of motion.
The concept portion of the test will stress:
•
Understanding the relationship between weight, mass, and inertia.
•
Correctly identifying third law action and reaction force pairs and how & why they don’t cancel.
•
The application of second and third laws of motion to collisions.
•
Distinguishing between “motion” and acceleration.
To help you with the quantitative aspect of the test, below are some sample problems from old tests. They
are grouped into three categories; it is important that you work enough problems from each category to
master the approach for that type of problem.
Students who do not complete the practice problems on their own, but merely watch them being worked in
class, fare poorly on this test.
PROBLEMS INVOLVING DIRECTLY OPPOSING FORCES
1.
A 20 kg crate hangs at the end of a long rope. Find the size and direction of its acceleration when the tension in the rope
is 250 N.
2.
A man weighing 160 lb stands on the floor of an elevator which descends at 1.00 ft/s2.
a) What amount of force will his feet exert upon the floor?
b) What amount of force will his feet exert when the elevator is ascending at 1.00 ft/s2?
3.
An elevator starts from rest with a constant upward acceleration. It moves 2.0 m in the first 0.60 seconds. A passenger
in the elevator is holding a 3.0 kg package by a vertical string. What is the amount of tension in the string during the
elevator's acceleration?
4.
At a physics convention, Mr. M met the lovely Netta Force. As they were ascending in a hotel elevator, Netta tested his
physics acumen. She said, "I would guess that you weigh 675 N. What is this elevator's rate of acceleration if you are
now exerting 715 N of force on the floor?" If Mr. M wants to score some points with Netta, what should he say?
1.
2.
3.
“It 4i.s
2.7 m/s2 up
a) 155 lb
b) 165 lb
63 N
intuitively obvious,
even to the most casual
observer, that we are both
rising at 0.581 m/s 2.”
Opposing Forces Answers:
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PROBLEMS INVOLVING ANGLED FORCES
5.
Victor Vector was dragging a 20.0 kg bundle of books with a rope as shown in the diagram. If the rope
s angled at 40.0E to the horizontal and had a tension of 80.0 N, and the friction between the books
d floor was 20.0 N, what was the magnitude of the acceleration of the towed tomes?
wa
an
6.
A construction worker attempts to pull a stake out of the ground by pulling on a rope that
is attached to the stake and makes an angle of 60.0E with the ground. If the stake has a mass of 1.00 kg and the friction
force holding it in the hole is 70.0 N straight downward, how much force must the worker apply to the rope to pull the
stake upward at a constant speed? (Do not concern yourself with normal forces here.)
7.
Suppose that a 70.0 kg box is pulled across a rough floor by a 400 N force at an angle of 30.0E above the horizontal.
If the frictional force on the box is 243 N, how much will the box accelerate?
8.
A 10.0 N picture is suspended by two wires of equal length which each make an angle of 20.0E with the horizontal. What
is the amount of tension in each wire?
5. 2.06 m/s2
6. 92.1 N
7. 1.48 m/s2
8. 14.6 N
Angled Forces Answers:
PROBLEMS INVOLVING INCLINED PLANES
9.
A 2.0 kg block is on a smooth plane inclined at a 30E angle from the horizontal. A light rope, tied to the block and
parallel with the plane, keeps the block from sliding.
a) Find the amount of tension in the rope required to keep the block from sliding down the plane.
b) Find the magnitude of the normal force exerted by the plane on the block.
c) Find the acceleration vector of the block when the rope is cut.
10.
Velma Velocity placed a 20 kg bundle of physics books on an inclined plane that was angled up
from the ground at 45E as shown at right. If the frictional force between the books and the plane
was 10 N, what was the acceleration vector of the tumbling tomes?
11.
Mr. M and his friend Fanny Friction were playing at the park one day. Extensive
experimentation revealed that a frictional force of 305 N existed between Fanny (mass 65.0 kg)
and a slide angled at 50.0E to the ground. Mr. M predicted Fanny's acceleration down the slide.
What value did he find?
9. a) 9.8 N
b) 17 N
c) 4.9 m/s 2 down the slope
10. 6.4 m/s2 down the plane
11. 2.81 m/s2
Inclined Planes Answers:
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CONCEPTS PRACTICE
In the space to the left, write the letter of the best answer to each question.
12. The Voyager I space probe, launched in 1977, passed the orbit of Pluto long ago and has traveled farther than any
other man-made object. What is needed to maintain the probe's velocity now that it is approaching "outer space"?
A) nothing is needed
B) enough thrust to balance its inertia
C) a tiny unbalanced force
D) enough thrust to balance the probe's large weight
13. A constant force F is applied to an object of mass m as it starts from rest and travels a distance d; the object's final
speed is vf . What is the new final speed if an object with half the mass (m/2) starts from rest, is pushed by the
force F, and travels the distance d?
A)
B)
C)
D)
14. A 10 kg brick and a 1 kg book are dropped near the earth's surface. The acceleration due to gravity of the 10 kg
brick is...
A) 10 times larger than the acceleration of the 1 kg book.
B) the same as the acceleration of the 1 kg book.
C) 10 times smaller than the acceleration of the 1 kg book.
D) zero.
15. Mr. M pulls Fluffy across the floor by her leash, accelerating her at a constant rate. Soon Fluffy digs in her claws,
applying a force that exactly balances the pull of the leash. She will now...
A) remain at a constant velocity. B) slow down. C) speed up.
16. Compared to an object weighing 10 N on earth, an object weighing 10 N on the moon would have...
A) less inertia. B) the same inertia.
C) more inertia.
17. Compared to a 10 kg object on earth, a 10 kg object on the moon would have...
A) less inertia. B) the same inertia.
C) more inertia.
18. The moon is attracted toward the earth by a large gravitational force. The earth is attracted toward the moon by
a force that is...
A) larger than its force on the moon.
B) the same size as its force on the moon.
C) smaller than its force on the moon.
D) zero.
19. A force accelerates a mass at a certain rate. If the mass were doubled and the force were halved, the acceleration
would then be...
A) quadrupled.
B) the same.
C) halved.
D) quartered.
Conceptual
Answers:
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12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
21. A lump of clay is thrown at a wall. The clay splats and sticks to the wall. The wall is
motionless...
A) because its greater inertia caused it to apply a larger force on the clay than the clay
applied to the wall.
B) because the action of the clay and reaction of the wall were equal and opposite and
cancelled out.
C) even though it was pushed by the clay just as much as the wall pushed on the clay.
A
D
B
A
C
B
B
D
D
C
20. A tablecloth can be withdrawn from under a glass without toppling it if the tablecloth is
jerked quickly. The reason this can be done is that the quick pull...
A) overcomes the inertial tendency of the glass.
B) creates a third-law reaction force that holds the glass in place.
C) creates a lot of friction which holds the glass in place.
D) does not overcome the inertial tendency of the glass.
OPTIONAL ADDITIONAL PRACTICE IF YOU NEED IT
DIRECTLY OPPOSING FORCES
22.
A small 150 g pebble is 3.40 km deep in the ocean and is falling with a constant terminal speed of 25.0 m/s. What is
the size and direction of the water’s force?
23.
Compute the magnitude of the initial upward acceleration of a rocket of mass 1.30×104 kg if the initial upward thrust
of its engine is 2.60×105 N. Do not neglect the weight of the rocket.
24.
A balloon weighing 1960 N is descending with an acceleration of 2.50 m/s2. What is the magnitude and direction of
the "lift" on the balloon? ("Lift" is a term for the force provided by the hot air in such a balloon.)
ANGLED FORCES
25.
A 10.0 kg mass is suspended by three cables as shown in the diagram at right. What
amount of force is exerted by each cable?
26.
A package is hanging from three ropes as shown. The vertical rope (B) is supporting half
of the package's 88.0 N weight. The other two ropes (A and C) are together supporting
the other half of the weight. Draw a free-body diagram of the package and then calculate
the magnitude of the overall tension in either rope A or C.
INCLINED PLANES
27.
A 100 lb block rests on a rough plane inclined 30E to the horizontal. If the frictional force between the block and the
plane is 22 lb, how much force must be applied parallel to the plane to cause the box to move up the plane at a constant
speed?
28.
A frictionless inclined plane makes an angle of 30.0E with the horizontal. How much force, applied parallel to the
plane, is required to cause a 15.0 kg box to slide up the plane with an acceleration of 1.20 m/s2?
29.
A 24 kg box begins sliding down an incline with a speed of 1.5 m/s. The incline is
5.0 m long and makes an angle of 25E with the horizontal. A 60.0 N friction force
impedes the motion of the box.
a. Predict the speed of the box when it reaches the bottom of the incline.
b. How much would the box accelerate if there were NO frictional force?
c. How much normal force is applied to the box when it is on the incline?
b) 4.1 m/s 2
27. 72 lb
28. 91.5 N
29. a) 4.3 m/s
c) 210 N
25. A = 98.0 N; B = 139 N; C = 98.0 N
26. 22.8 N
22. 1.47 N upward
23. 10.2 m/s2
24. 1460 N upward
OPTIONAL Extra Practice Answers
Units 5-7 Test Review
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