Download Newton`s law

SELECTED PROBLEMS ON KINEMATICS
AND NEWTON'S LAWS
1) A motorist travels for 3.0 h at 80 km/h and 2.0 h at
100 km/h. What is her average speed for the trip?
A) 85 km/h
B) 88 km/h
C) 90 km/h
D) 92 km/h
Answer: B
2) If you run a complete loop around an outdoor track
(400 m), in 100 s, your average velocity is
A) 0.25 m/s.
B) 4.0 m/s.
C) 40,000 m/s.
D) zero.
Answer: D
3) A car traveling 60 km/h accelerates at the rate of
2
2.0 m/s . How much time is required for the car to
reach a speed of 90 km/h?
A) 15 s
B) 30 s
C) 45 s
D) 4.2 s
Answer: D
4)A cart with an initial velocity of 5.0 m/s experiences
2
a constant acceleration of 2.0 m/s . What is the cart's
displacement during the first 6.0 s of its motion?
A) 10 m
B) 55 m
C) 66 m
D) 80 m
Answer: C
5) An object is thrown upward with a speed of 12 m/s
on the surface of planet X where the acceleration due
2
to gravity is 1.5 m/s . What is the maximum height
reached by the object?
A) 8.0 m
B) 18 m
C) 48 m
D) 144 m
Answer: C
6) A ball is thrown upward at a velocity of 19.6 m/s.
What is its velocity after 3.00 s?
A) 9.8 m/s upward
B) 9.8 m/s downward
C) zero
D) 19.6 downward
Answer: B
7) If the acceleration of an object is always directed
perpendicular to its velocity,
A) the object is speeding up.
B) the object is slowing down.
C) the object is turning.
D) this situation would not be physically possible.
Answer: C
8) In the absence of an external force, a moving
object will
A) stop immediately.
B) slow down and eventually come to a stop.
C) go faster and faster.
D) move with constant velocity.
Answer: D
9) You are standing in a moving bus, facing forward,
and you suddenly fall forward. You can imply from
this that the bus's
A) velocity decreased.
B) velocity increased.
C) speed remained the same, but it's turning to the
right.
D) speed remained the same, but it's turning to the
left.
Answer: A
10)An object is initially located at the origin has an
2
acceleration of a = 2 j m/s and an initial velocity of
vi = 3 i m/s. Find the magnitude of the velocity of the
object at t = 2 seconds.
A) 5 m/s.
B) 7.8 m/s.
C) 5.8 m/s.
D) 25 m/s.
Answer: A
3
11)The position of an object is given by x = 2t ,
where x is measured in meters and t is measured in
seconds. What is the average velocity of the object
between t = 1 s and t = 3 s?
A) 185 m/s.
B) 26 m/s.
C) 30 m/s.
D) 28m/s.
Answer: B
12)A particle moves on a circular path according to
3
the relation θ(t) = 2 t -t where t is in seconds and θ is
in radians. What is the angular velocity of the particle
at t = 10 seconds?.
A) 600 rad/s
B) 599 rad/s
C)1999 rad/s
D)119 rad/s
Answer: A
13) A net force F acts on a mass m and produces an
acceleration a. What acceleration results if a
net force 2F acts on mass 4m?
A) a/2
B) 8a
C) 4a
D) 2a
Answer: D
14) If you blow up a balloon, and then release it, the
balloon will fly away. This is an illustration of
A) Newton's first law.
B) Newton's second law.
C) Newton's third law.
D) Galileo's law of inertia.
Answer: C
15) A 20-N weight and a 5.0-N weight are dropped
simultaneously from the same height. Ignore
air resistance. Compare their accelerations.
A) The 20 N weight accelerates faster because it is
heavier.
B) The 20 N weight accelerates faster because it has
more inertia.
C) The 5.0 N weight accelerates faster because it
has a smaller mass.
D) They both accelerate at the same rate because
they have the same weight to mass ratio.
Answer: D
16) An object of mass m is hanging by a string from
the ceiling of an elevator. The elevator is
moving upward, but slowing down. What is the
tension in the string?
A) less than mg
B) exactly mg
C) greater than mg
D) zero
Answer: A
23) A wheel accelerates with a constant angular
2
acceleration of 4.5 rad/s . If the initial angular
velocity is 1.0 rad/s, what is the angle the wheel
rotates through in 2.0 s?
A) 11 rad
B) 9.0 rad
C) 7.0 rad
D) 4.5 rad
Answer: A
17) A person on a scale rides in an elevator. If the
mass of the person is 60.0 kg and the elevator
accelerates downward with an acceleration of 4.90
m/s2, what is the reading on the scale?
A) 147 N
B) 294 N
C) 588 N
D) 882 N
Answer: B
24) A wheel accelerates with a constant angular
2
acceleration of 4.5 rad/s . If the initial angular
velocity is 1.0 rad/s, what is the angular velocity at t =
2.0 s?
A) 1.0 rad/s
B) 7.0 rad/s
C) 9.0 rad/s
D) 10 rad/s
Answer: D
18) A student pulls a box of books on a smooth
horizontal floor with a force of 100 N in a direction of
37e above the horizontal. If the mass of the box and
the books is 40.0 kg, what is the acceleration of the
box?
2
A) 1.5 m/s
2
B) 1.9 m/s
2
C) 2.0 m/s
2
D) 3.3 m/s
Answer: C
25) A wheel of diameter of 68.0 cm slows down
uniformly from 8.40 m/s to rest over a distance of 115
m. What is the total number of revolutions the wheel
rotates in coming to rest?
A) 53.8 rev
B) 26.9 rev
C) 338 rev
D) 169 rev
Answer: A
19) A traffic light of weight 100 N is supported by two
ropes as shown in the Fig.
What are the tensions in the ropes?
A) 50 N
B) 63 N
C) 66 N
D) 83 N
Answer: D
20) Two boxes of masses m and 2m are in contact
with each other on a frictionless surface. (SeeFig.)
What is the acceleration of the more massive box?
A) F/m
B) F/(2m)
C) F/(3m)
D) F/(4m)
Answer: C
21) Consider a particle moving with constant speed
such that its acceleration of constant
magnitude is always perpendicular to its velocity.
A) It is moving in a straight line.
B) It is moving in a circle.
C) It is moving in a parabola.
D) None of the above is definitely true all of the time.
Answer: B
22) An object moves with a constant speed of 30 m/s
on a circular track of radius 150 m. What is the
acceleration of the object?
A) zero
2
B) 0.17 m/s
2
C) 5.0 m/s
2
D) 6.0 m/s
Answer: D
26) In the Atwood machine shown in the Fig, if M =
0.60 kg and m = 0.40 kg, what is the magnitude of
the acceleration of the system? (Ignore friction and
the mass of the pulley.)
2
A) 5.3 m/s
2
B) 3.9 m/s
2
C) 2.0 m/s
2
D) 0.98 m/s
Answer: C
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