Download Physics: Principle and Applications, 7e (Giancoli) Chapter 4

Physics: Principle and Applications, 7e (Giancoli)
Chapter 4 Dynamics: Newton's Laws of Motion
4.1 Conceptual Questions
1) In a collision between a huge SUV and a small hybrid car, the SUV exerts a larger force on
the hybrid than the hybrid exerts on the SUV.
A) True
B) False
C) It depends on whether the collision is a head-on collision or a rear-end collision.
Answer: B
Var: 1
2) A box is placed on a table which rests on the floor. The box pushes on the table; the reaction
force to the box's push on the table is the table's push on the floor.
A) True
B) False
Answer: B
Var: 1
3) In order to get an object moving, you must push harder on it than it pushes back on you.
A) True
B) False
Answer: B
Var: 1
4) A girl attaches a rock to a string, which she then swings counter-clockwise in a horizontal
circle. The string breaks at point P in the figure, which shows a bird's-eye view (as seen from
above). Which path (A-E) will the rock follow?
A) Path A
B) Path B
C) Path C
D) Path D
E) Path E
Answer: B
Var: 1
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8) In order to lift a bucket of concrete, you must pull up harder on the bucket than the bucket
pulls down on you.
A) True
B) False
Answer: B
Var: 1
9) If the rockets of a spaceship in outer space (far from all gravity) suddenly lose power and go
off, the spaceship will gradually slow to a stop.
A) True
B) False
Answer: B
Var: 1
10) You are in a train traveling on a horizontal track and notice that a piece of luggage starts to
slide directly toward the front of the train. From this observation, you can conclude that this train
is
A) speeding up.
B) slowing down.
C) changing direction.
D) speeding up and changing direction.
E) slowing down and changing direction.
Answer: B
Var: 1
11) While flying horizontally in an airplane, you notice that a string dangling from the overhead
luggage compartment hangs at rest at 15° away from the vertical toward the front of the plane.
Using this observation, you can conclude that the airplane is
A) moving forward.
B) moving backward.
C) accelerating forward.
D) accelerating backward.
E) not accelerating because the string is at rest.
Answer: D
Var: 1
12) An elevator suspended by a vertical cable is moving downward but slowing down. The
tension in the cable must be
A) greater than the weight of the elevator.
B) less than the weight of the elevator.
C) equal to the weight of the elevator.
Answer: A
Var: 1
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14) A bucket is being lowered by a very light rope with a constant downward velocity. The
tension in the rope must be
A) equal to the weight of the bucket.
B) greater than the weight of the bucket.
C) less than the weight of the bucket.
Answer: A
Var: 1
17) A small car and a large SUV are at a stoplight. The car has a mass equal to half that of the
SUV, and the SUV can produce a maximum accelerating force equal to twice that of the car.
When the light turns green, both drivers push their accelerators to the floor at the same time.
Which vehicle pulls ahead of the other vehicle after a few seconds?
A) The car pulls ahead.
B) The SUV pulls ahead.
C) It is a tie.
Answer: C
Var: 1
27) A fireman is sliding down a fire pole. As he speeds up, he tightens his grip on the pole, thus
increasing the vertical frictional force that the pole exerts on the fireman. When the force on his
hands equals his weight, what happens to the fireman?
A) The fireman comes to a stop.
B) The fireman descends with slower and slower speed.
C) The fireman descends with a smaller but non-zero acceleration.
D) The fireman continues to descend, but with constant speed.
E) The acceleration of the fireman is now upward.
Answer: D
Var: 1
28) A person is using a rope to lower a 5.0-N bucket into a well with a constant speed of 2.0 m/s.
What is the magnitude of the force exerted by the rope on the bucket?
A) 0.00 N
B) 2.0 N
C) 5.0 N
D) 10 N
E) 49 N
Answer: C
Var: 1
29) A person who normally weighs 700 N is riding in a rather swift elevator that is moving at a
constant speed of 9.8 m/s. If this person is standing on a bathroom scale inside the elevator, what
would the scale read?
A) more than 700 N
B) less than 700 N
C) 700 N
D) It could be more or less than 700 N, depending on whether the elevator is going up or down.
Answer: C
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Var: 1
31) A 75-N box rests on a perfectly smooth horizontal surface. The minimum force need to start
the box moving is
A) 75 N.
B) 7.5 N.
C) 750 N.
D) any horizontal force greater than zero.
Answer: D
Var: 1
[Two Tipers Problems B3-RT08 and B3-RT12]
34) When a 45-kg person steps on a scale in an elevator, the scale reads a steady 410 N. Which
of the following statements must be true? (There could be more than one correct choice.)
A) The elevator is accelerating upward at a constant rate.
B) The elevator is accelerating downward at a constant rate.
C) The elevator is moving upward at a constant rate.
D) The elevator is moving downward at a constant rate.
E) From the given information, we cannot tell if the elevator is moving up or down.
Answer: B, E
Var: 1
35) Inside of a train a ball of weight W is hanging by a light wire at rest from the ceiling. The
wire makes an angle θ with the ceiling, as shown in the figure. Which one of the following
conditions must be true about the tension T in the wire?
A) T sin θ = W
B) T cos θ = W
C) T tan θ = W
D) T = W
E) T = ma
Answer: A
Var: 1
39) As shown in the figure, a woman is straining to lift a large crate, but without success because
it is too heavy. We denote the forces on the crate as follows: P is the magnitude of the upward
force being exerted on the crate by the person, C is the magnitude of the vertical contact force on
the crate by the floor, and W is the weight of the crate. How are the magnitudes of these forces
related while the person is trying unsuccessfully to lift the crate?
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A) P + C = W
B) P + C < W
C) P + C > W
D) P = C
Answer: A
Var: 1
40) A push of magnitude P acts on a box of weight W as shown in the figure. The push is
directed at an angle θ below the horizontal, and the box remains a rest. The box rests on a
horizontal surface that has some friction with the box. The normal force on the box due to the
floor is equal to
A) W.
B) W + P.
C) W + P cos θ.
D) W + P sin θ.
E) W - P sin θ.
Answer: D
Var: 1
41) A push of magnitude P acts on a box of weight W as shown in the figure. The push is
directed at an angle θ below the horizontal, and the box remains a rest. The box rests on a
horizontal surface that has some friction with the box. The friction force on the box due to the
floor is equal to
A) P sin θ
B) P cos θ
C) 0
D) P cos θ + W
E) P + W
Answer: B
Var: 1
42) In the figure, what does the spring scale read? The pulleys are ideal and the strings and scale
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are also massless.
A) exactly 2.0 N.
B) exactly 1.0 N
C) 0.50 N
D) 0.00 N
E) more than 19.6 N
Answer: B
Var: 1
43) Two boxes P and Q on a perfectly smooth horizontal surface are connected by a light
horizontal cord. The mass of P is greater than that of Q. A horizontal force is applied to box Q
as shown in the figure, accelerating the bodies to the right. The magnitude of the force exerted by
the connecting cord on body P is
A) zero.
B) less than F but not zero.
C) equal to F.
D) greater than F.
Answer: B
Var: 1
44) Three boxes are pulled along a horizontal frictionless floor by a constant horizontal pull P.
The boxes are connected by very light horizontal strings having tensions T1 and T2 as shown in
the figure. Which of the following statements about the tensions is correct? (There could be more
than one correct choice.)
A) T1 = P
B) T2 = P
C) T1 + T2 = P
D) T2 > T1
E) T1 > T2
Answer: E
Var: 1
46) Two boxes are connected to each other by a string as shown in the figure. The 10-N box
slides without friction on the horizontal table surface. The pulley is ideal and the string has
negligible mass. What is true about the tension T in the string?
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A) T = 10 N
B) T = 20 N
C) T = 30 N
D) T < 30 N
E) T > 30 N
Answer: D
Var: 1
4.2 Problems
1) What is the mass of an object that experiences a gravitational force of 685 N near Earth's
surface where g = 9.80 m/s2?
A) 69.9 kg
B) 68.5 kg
C) 71.3 kg
D) 72.7 kg
Answer: A
Var: 50+
2) If I weigh 741 N on Earth at a place where g = 9.80 m/s2 and 5320 N on the surface of another
planet, what is the acceleration due to gravity on that planet?
A) 70.4 m/s2
B) 51.4 m/s2
C) 61.2 m/s2
D) 81.0 m/s2
Answer: A
Var: 50+
9) A 40-kg crate is being lowered with a downward acceleration is 2.0 m/s2 by means of a rope.
(a) What is the magnitude of the force exerted by the rope on the crate?
(b) What would be the magnitude of the force exerted by the rope if the crate were being raised
with an acceleration of 2.0 m/s2?
Answer: (a) 310 N (b) 470 N
Var: 1
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13) A certain aircraft has a mass of 300,000 kg. At a certain instant during its landing, its speed
is 27.0 m/s. If the braking force is a constant 445,000 N, what is the speed of the airplane 10.0 s
later?
A) 10.0 m/s
B) 12.2 m/s
C) 14.0 m/s
D) 18.0 m/s
E) 20.0 m/s
Answer: B
Var: 5
21) A box of mass 72 kg is at rest on a horizontal frictionless surface. A constant horizontal force
of magnitude F then acts on the box, accelerating it to the right. You observe that it takes the box
3.4 seconds to travel 13 meters. What is the magnitude of the force F?
Answer: 160 N
Var: 50+
27) The figure shows an acceleration-versus-force graph for a 125-g object. What should be the
value of the first tick-mark on the vertical scale, as indicated by the arrow in the figure?
A) 4
B) 8
C) 0.00400
D) 0.00800
Answer: A
Var: 12
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29) The figure shows an acceleration-versus-force graph for three objects pulled by wires. If the
mass of object 2 is 36 kg, what are the masses of objects 1 and 3?
A) 12 kg and 90 kg
B) 72 kg and 18 kg
C) 90 kg and 12 kg
D) 12 kg and 72 kg
Answer: A
Var: 1
35) A 30.0-kg load is being held in place using massless wires in the ideal pulley arrangement
shown in the figure. What is the magnitude of the force F?
Answer: 147 N
Var: 1
58) The figure shows a 100-kg block being released from rest from a height of 1.0 m. It then
takes 0.53 s for it to reach the floor. What is the mass m of the block on the left? There is no
friction or mass in the pulley, and the connecting rope is very light.
A) 16 kg
B) 14 kg
C) 13 kg
D) 11 kg
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Answer: A
Var: 50
60) In the figure, block A has a mass of 3.00 kg. It rests on a smooth horizontal table and is
connected by a very light horizontal string over an ideal pulley to block B, which has a mass of
2.00 kg. When block B is gently released from rest, how long does it take block B to travel 80.0
cm?
A) 0.404 s
B) 0.494 s
C) 0.639 s
D) 0.785 s
E) 0.935 s
Answer: C
Var: 5
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