Download PHYSICS 2325 EXAM 2 REVIEW

PHYSICS 2325 EXAM 2 REVIEW
1. A body moves in a circle at constant speed. The work done on the body by the
centripetal force in one revolution is
a. zero.
b. F 2 r .
c. Ft.
b g
v2
.
r
mv 2
e.
.
r
d.
ANS: a
7. When a 4.0 kg mass is raised from the floor and set on a table 1.2 m above the floor,
the net work done on the mass by all forces is
a. –47 J.
b. –4.8 J.
c. 0 J.
d. 4.8 J.
e. 47 J.
ANS: c
10. When a 0.16 kg baseball starts from rest and is accelerated to a speed of 35 m/s, how
much net work in J is done on the ball?
a. 10
b. 50
c. 98
d. 120
e. 196
ANS: c
20. A body is displaced 1.5i  2.0j m while being acted on by the force 2.0i  3.0j N .
e
j
e
j
How much work is done on the body by the force?
a. 6
b. 7
c. 8
d. 9
e. 10
ANS: d
24. An object moves from x  0 m to x  7 m subject to the force shown in the diagram.
How much work in J is done on the object by the force when the object moves from
x  0 m to x  1 m ?
F( x) (N)
40
20
0
1
2
3
4
5
6
7
x (m)
–20
–40
a. –40
b. –20
c. 0
d. 20
e. 40
ANS: d
27. An object moves from x  0 m to x  7 m subject to the force shown in the diagram.
How much work in J is done on the object by the force when the object moves from
x  5 m to x  4 m ?
F( x) (N)
40
20
0
1
2
3
4
5
6
7
x (m)
–20
–40
a. –40
b. –20
c. 0
d. 20
e. 40
ANS: d
32. A 12.0 kg block is moved up a 20.0° incline. A 1.10 N frictional force is exerted on
the block by the plane. How much work against friction is done on the block to move it
3.00 m up the plane?
a. 0.816
b. 0.923
c. 1.10
d. 3.30
e. 4.20
ANS: d
38. Starting from rest at t  0 , a 2.0 kg block is pushed across a horizontal surface by a
force directed as shown F  8.0 N . The magnitude of the resulting acceleration of the
block is 2.0 m s 2 . At what rate in W is the force of friction doing work on the block at
t  3.0 s ?
a
f

F
40°
a. +13
b. +24
c. –24
d. –2.1
e. –13
ANS: e
43. During the time a 2.0 kg projectile moves from its initial position to a point that is
displaced 20 m horizontally and 15 m above its initial position, how much work in J is
done by the gravitational force on the projectile?
a. 0.29  103
b. 0.29  103
c. +30
d. –30
e. –50
ANS: b
47. A 1.4 kg block is pushed up a frictionless 14° incline from point A to point B by a
force P as shown in the figure. Points A and B are 1.2 m apart. If the kinetic energies of
the block at A and B are 3.0 J and 4.0 J, respectively, how much work in J is done on the
block by the force P between A and B?
P
B
14° A
a. 7.2
b. 3.0
c. 5.0
d. 1.0
e. 4.0
ANS: c
54. A person runs up an escalator at twice the speed of the escalator. How much work did
the escalator’s motor do compared to the work the motor would have done if s/he would
have stood still?
a. The motor did more work.
b. The motor did the same work.
c. The motor did less work.
d. Can’t determine the answer from the information given.
ANS: c
64. Two blocks are pushed across a level surface by a 60 N horizontal force as shown
below. The coefficient of kinetic friction between the blocks and the surface is 0.250.
When the blocks have been displaced 5.00 m to the right, the work (in J) done on the 4.00
kg block by the 60.0 N force is
60.0 N
2.00 kg
4.00 kg
a. 0
b. 75.5
c. 300
d. 600
e. 900
ANS: a
67. John has two 100 W bulbs on in his room. His stereo is on and is using another 100
W. His computer and monitor are using 300 W. His minifridge is using another 200 W. If
a kW/hr of electrical energy costs 15 cents, what is he charged for 6 hours worth of
energy?
a. 10.5 cents
b. 72 cents
c. $1.05
d. $72.00
e. $1.75
ANS: b
72. A freight car loaded with ore is sitting on a 5° incline when its brakes fail. After
traveling 150 m on a frictionless track, it reaches level ground where it strikes a massive
safety spring of spring constant k  18 ,500 N m . When its velocity has decreased to zero,
an automatic latch will catch the car. The equation that can be solved for the car’s kinetic
energy just before striking the spring is
1
1
a. mv 2f  mgh f  mv i2  mghi .
2
2
1
1
2
b. mv f  mgh f  mv i2 .
2
2
1
1
1 2
2
c. mv f  mgh f  mv i2  kx max
.
2
2
2
1
1 2
mv 2f  mgh f  kx max
 mghi .
2
2
1
1
1
1
e. mv 2f  mgh f  kx 2f  mv i2  mghi  kx i2 .
2
2
2
2
d.
ANS: a

77. A 150 g baseball is thrown with initial velocity v  8.00i  19.6j m s . What is its
e
j
kinetic energy when at the highest point of its trajectory?
a. 4.8
b. 33.6
c. 57.1
d. 67.2
e. 33,600
ANS: a
79. A thin plate of negligible mass is attached to the end of spring A, which has
k  1380 N m . The end with the plate is pressed against an identical spring B fastened to a
wall until the force exerted on the end of A is 225 N. By how much has spring B been
compressed from its unstretched length?

Fapplied
A
B
a. 0.0815 m
b. 0.163 m
c. 0.326 m
d. 1.63 m
e. 6.13 m
ANS: b
82. A mechanical door opener is used to deliver power to a spring with spring constant k
for t seconds. The equation we would use to find the compression of the spring at the end
of the t seconds is
a. P  kx .
b. Pt  kx .
P 1
c.  kx 2 .
t
2
1 2
d. P  kx .
2
1
e. Pt  kx 2 .
2
ANS: e
2. The motion of a ball of mass m dropped off a building is observed by a man at ground
level and a woman at the top of the building. The man’s origin for measuring
gravitational potential energy is at ground level and the woman’s origin for measuring
gravitational potential energy is at the top of the building. The building’s height is h and
air friction is neglected. What potential energy does the man record after the ball has
fallen a distance d?
a. mgh
b. –mgd
c. mgd
d. mg h  d
e. zero
a f
ANS: d
4. The motion of a ball of mass m dropped off a building is observed by a man at ground
level and a woman at the top of the building. The man’s origin for measuring
gravitational potential energy is at ground level and the woman’s origin for measuring
gravitational potential energy is at the top of the building. The building’s height is h and
air friction is neglected. What change in potential energy does the woman record after the
ball has fallen a distance d?
a. mgh
b. –mgd
c. mgd
d. mg h  d
e. zero
a f
ANS: b
8. An object of mass m is lifted a height y from the floor to a table by a woman. How
much work did she do?
a. mgy
b. –mgy
1
c. mv 2
2
1
2
d.  mv 2
e. zero
ANS: a
11. A woman lifts a shoebox of mass m a distance y from the floor to a closet shelf. How
much work was done by gravity?
a. mgy
b. –mgy
1
c. mv 2
2
1
2
d.  mv 2
e. zero
ANS: b
14. Which of the following is in stable equilibrium?
a. A ball on the floor
b. A pyramid resting on its base
c. A spinning top
d. A coin standing on edge
e. A nail balanced on its point
ANS: b
18. What kinetic energy in J does an 8.24  10 4 kg airliner have when moving at a speed of
630 km/hr?
a. 1.93  10 6
b. 1.78  10 7
c. 1.83  10 8
d. 1.26  10 9
e. 1.87  1010
ANS: d
22. A 50 kg boy is on a massless swing that has an effective length of 3.0 m. His potential
energy is zero when the angle between the swing and the vertical is zero. The maximum
angle between the swing and the vertical is 35°? What is his speed in m/s at the bottom of
the swing?
a. 6.9
b. 6.2
c. 5.1
d. 4.2
e. 3.3
ANS: e
26. The conservative force F   4.0x  3.0 N does work on a particle moving along the xaxis. How much work in J is done on the particle by this force when the particle moves
from x  2.0 m to x  3.0 m ?
a. 12
b. 13
c. 14
d. 15
e. 16
ANS: b
29. When released, a bead slides without friction down a wire and makes a loop–the–loop
as shown in the diagram. What is its speed in m/s at the top of the circular loop?
bead
6.0 m
2.0 m
a. 6.3
b. 7.4
c. 8.9
d. 11
e. 13
ANS: a
36. Three charges of 3.01  10 6 C are assembled in an equilateral triangle with sides of
0.0121 m. How much work in J is needed to do this? k e  8.99  10 9 Nm 2 C 2
a. 3.61
b. 6.73
c. 13.5
d. 20.2
e. 21.0
e
j
ANS: d
41. A 0.80 kg object tied to the end of a 2.0 m string swings as a pendulum. At the lowest
point of its swing, the object has a kinetic energy of 10 J. Determine the speed of the
object in m/s at the instant when the string makes an angle of 50° with the vertical.
a. 5.6
b. 4.4
c. 3.3
d. 5.0
e. 6.1
ANS: c
46. As a 1.5 kg mass moves along the x axis, it is acted upon by a single conservative
force given by Fx  6x 2 N , where x is in m. At x  0 (where its speed is 4.0 m/s), the
potential energy associated with the force is +30 J. What is the potential energy in J at
x  2.0 m ?
a. –16
b. +46
c. +36
d. +14
e. –28
ANS: d
53. The equation that states mathematically the principle of conservation of mechanical
energy for an isolated system is
a. K f  Ki .
b. U f  U i .
c. K f  U f  Ki  U i .
d. K f  Ki  U f  U i .
e. K f  U f  W  Ki  U i .
ANS: c
55. What is the minimum speed (in m/s) with which a spaceship must leave the surface of
the Earth in order to be able to escape the gravitational attraction of the Earth?
G  6.67  10 11 Nm 2 kg 2 , M Earth  5.98  10 24 kg , R Earth  6.37  10 6 m , m ship  2000 kg
a. 4.21  10 4
b. 1.12  10 4
c. 5.00  10 4
d. 4.43
e. 2.05  10 7
ANS: b
62. A person of mass m stands in an elevator that is at rest at the position where
gravitational potential energy is taken to be zero. The elevator then accelerates upwards
with acceleration a. When the elevator has risen a distance h, the person’s total
mechanical energy is
a. 0.
b. mgh.
c. mah.
d. a  g mh .
e. a  g mh .
b g
b g
ANS: d
63. A person of mass m stands in an elevator that is at rest at the position where
gravitational potential energy is taken to be zero. The elevator then descends with
acceleration a. When the elevator has descended a distance h, the person’s total
mechanical energy is
a. 0.
b. –mgh.
c. mah.
d. a  g mh .
e. a  g mh .
b g
b g
ANS: e
66. A car starts at height h above ground and rolls around the loop-the-loop of radius R.
We want to calculate h in terms of R for the car just to make it around without losing
contact with the track. Assume the track is frictionless. Which equation below must be
one of the equations we use to solve this problem? (Use v top as the speed at the top of the
circular loop and v bottom as the speed at the bottom of the circular loop.)
bead
h
2.0 m
2
2
a. v bottom
 v top
 gR
2
2
b. v bottom  v top  2 gR
2
2
c. v bottom
 v top
 gR
2
2
d. v bottom  v top  2 gR
2
2
e. v bottom
 v top
 5 gR
ANS: b
70. A light string suspended over a frictionless pulley of negligible mass connects a 20 kg
and a 12 kg mass as shown below. When they are released from rest, and the 20 kg mass
has fallen 1.0 m, the speed of the 12 kg mass, in m/s, is
12 kg
20 kg
a. 1.1.
b. 1.6.
c. 2.2.
d. 3.1.
e. 4.9.
ANS: c
1. What is the ratio of the kinetic energy of a body of mass m and speed v to the
magnitude of its momentum?
v
a.
2
b. v
3v
c.
2
d. 2v
5v
e.
2
ANS: a
4. The speed of a body changes from v 0 to 2 v 0 . Its momentum changes in magnitude
from p 0 to _____ p 0 .
a. 1/4
b. 1/2
c. 1
d. 2
e. 4
ANS: d
7. A sphere of radius 2 m which has its diameter collinear with the z-axis is located above
the xy plane and is tangent to the xy plane at the origin (0, 0, 0). The coordinates of its
center of mass, in m, are
a. 0, 0, 2.
b. 2, 0, 0.
c. 0, 2, 0.
d. 2, 2, 0.
e. 2, 2, 2.
ANS: a
11. A circular plate of radius 3.0 m is located with its center on a line at 45° to the x axis.
The circle is tangent to both the x and y axis as shown. What are the coordinates in m of
its center of mass?
y
x
a. 2, 1
b. 1, 2
c. 2, 4
d. 3, 3
e. 3, 6
ANS: d
17. A 3.0 kg block moving at 5.0 m/s catches up with a 5.0 kg block moving in the same
direction at 3.0 m/s. They stick together. At what speed, in m/s, do they move after
sticking together?
a. 2.5
b. 3.8
c. 2.9
d. 4.1
e. 3.5
ANS: b
19. A 5.00 kg body is acted on by a horizontal force as shown in the graph. What impulse
in kg  m s is transmitted to the body by the force?
F(N)
5
4
3
2
1
0
1
2
3
4
5
6
7
8
t (s)
a. 15.5
b. 7.50
c. 17.5
d. 32.5
e. 27.5
ANS: e
21. What average horizontal force in N is experienced by a 5 kg object when acted on by
the force shown below from t  0 s to t  4 s ?
F(N)
6
2
a. 1.0
b. 2.0
c. 3.0
d. 4.0
e. 5.0
ANS: c
4
6
8
10
12
t (s)
25. A 0.0111 kg bullet hits a 5.25 kg block. The two move off together at a speed of 7.35
m/s. What was the speed of the bullet in m/s before the collision?
a. 1.97  10 3
b. 9.23  10 2
c. 2.89  10 3
d. 3.48  10 3
e. 3.88  10 3
ANS: d
28. Two balls of equal mass, A and B, have velocities of 6 i m s and 4i m s , respectively.
If they collide elastically, what are their velocities in m/s after the collision? Ball A’s
velocity is listed first.
a. 6 i ,  4i
b. 4i , 6 i
c. 6 i ,  4j
d. 4j, 6 j
e. 6 j,  4j
ANS: b
32. Object A, whose center is at (2.0m, 2.0m) has a mass of 40 kg. Object B has its center
at (10m, 4.0m) and has a mass of 30 kg. What is the y component of their center of mass
in m?
y (m)
B
4
2
0
A
2
4
6
8
10
x (m)
a. 2.9
b. 5.4
c. 6.1
d. 6.3
e. 6.7
ANS: a
38. An 8.0 kg object moving 4.0 m/s in the positive x direction has a one-dimensional
collision with a 2.0 kg object moving at 3.0 m/s in the opposite direction. The final
velocity of the 8.0 kg object is 2.0 m/s in the positive x direction. What is the total kinetic
energy in J of the two-mass system after the collision?
a. 32
b. 52
c. 41
d. 25
e. 29
ANS: c
43. A 2000 kg truck traveling at a speed of 6.0 m/s makes a 90° turn in a time of 4.0 s and
emerges from this turn with a speed of 4.0 m/s. What is the magnitude of the average
resultant force in kN on the truck during this turn?
a. 4.0
b. 5.0
c. 3.6
d. 6.4
e. 0.67
ANS: c
46. The only force acting on a 2.0 kg object moving along the x axis is shown. If the
velocity v x is 2.0 m s at t  0 , what is the velocity in m/s at t  4.0 s ?
Fx (N)
8
4
0
t (s)
1
2
3
4
–4
–8
a. –2.0
b. –4.0
c. –3.0
d. +1.0
e. –5.0
ANS: e
50. A 3.0 kg ball with an initial velocity of 4i  3 j m s collides with a wall and rebounds
e j
e
j
with a velocity of 4i  3j m s . What is the impulse in N  s exerted on the ball by the
wall?
a. 24i
b. 24i
c. 18 j
d. 18 j
e. 8 i
ANS: b
53. In an elastic collision
a. only energy is conserved.
b. only momentum is conserved.
c. only force is conserved.
d. both momentum and energy are conserved.
e. both force and momentum are conserved.
ANS: d
61. Two bodies, A and B, arrive at the base of a frictionless inclined plane with equal
momenta of magnitude p. m B  2m A . The ratio of the time t B for B to reach its maximum
height to the time t A for A to reach its maximum height is
1
4
1
b. t B  t A .
2
c. t B  t A .
a. t B  t A .
d. t B  2t A .
e. t B  4t A .
ANS: b
69. A system initially consists of a ball of mass m at rest at height h above the Earth and
h
the Earth, of mass M E . When the ball has fallen a distance , the total momentum of the
2
system is
a. 0.
b. m 2 gh .
c. M E 2 gh .
d. M E  m 2 gh .
e. M E  m 2 gh .
b
b
g
g
ANS: a
81. Two birds of prey hurtling after the same mouse collide in mid-air and grab each
other with their talons. If each 250 g bird is flying at 30 m/s at a 60° angle to the ground,
what is the magnitude of their velocity, in m/s, immediately after the collision?
60°

v1
a. 0
b. 13
c. 15
d. 26
e. 30
ANS: d
60°

v2
4. When a wheel of radius R rotates about a fixed axis, a point R m from the center of the
wheel moves a distance of 4.0 m. How far in m does a point at a distance R 2 from the
center move in the same time?
a. 0.25
b. 0.33
c. 0.50
d. 1.0
e. 2.0
ANS: e
12. After starting from rest with constant angular acceleration, a wheel reaches a speed of
15.0 rad/s in 3.00 s. The angular acceleration in rad s 2 is
a. 3.
b. 5.
c. 7.5.
d. 15.
e. 21.
ANS: b
16. If   2  4t  8t 2 , the angular position in radians when t  3 s is
a. 74.
b. 86.
c. 82.
d. 38.
e. 36.
ANS: b
21. A wheel rotates from rest for 3.0 s with constant   4.0 rad s . What angle in radians
has it turned through?
a. 15
b. 18
c. 12
d. 21
e. 24
ANS: b
25. A 2.0 kg block is released from A on a frictionless track. Determine its linear speed in
m/s at P.
A
P
h =5m
R=2m
a. 16
b. 7.7
c. 8.8
d. 18
e. 9.9
ANS: b


29. Given r  2 i  j m and F  i  3j N , calculate the torque (in Nm) about the origin.
e j
e j
7k
5k
4k
a.
b.
c.
d. 6k
e. 6k
ANS: a
31. The moment of inertia of a body is 3.0 kg  m 2 . When its angular velocity is 6.0 rad/s,
its rotational kinetic energy in J is
a. 36.
b. 18.
c. 9.0.
d. 54.
e. 27.
ANS: d
36. Two blocks, m 1  1 kg and m 2  2 kg , are connected by a light string as shown in the
figure. If the radius of the pulley is 1 m and its moment of inertia is 5 kg  m 2 , the
acceleration of the system in g is
m1
m2
a. 1/6.
b. 3/8.
c. 1/8.
1
d. .
2
e. 5/8.
ANS: c
38. A pendulum bob of mass m is set into motion in a circular path in a horizontal plane
as shown in the figure. The square of the angular momentum of the bob about the vertical
axis through the point P is

l
P
a.
b.
c.
d.
e.
0
m 2 gl 3 sin 4 
.
cos 
m 2 gl 3 sin 3 
.
cos 
m 2 gl 3 sin 2 
.
cos 
m 2 gl 3 sin 
.
cos 
m 2 gl 2 sin 2  .
ANS: a
43. A mass of 1 kg is attached to a length of string that is wrapped several times around a
uniform solid cylinder of radius 1 m and moment of inertia of 3 kg  m 2 . Find the torque
on the cylinder in terms of kg  m g .
b g
a.
1
g
4
b. g
1
c. g
2
3
d. g
4
2
e. g
3
ANS: d
45. A solid cylinder of radius R  1 m and mass 10 kg rotates about its axis. When its
angular velocity is 10 rad/s, its angular momentum in kg  m 2 s is
a. 50.
b. 20.
c. 4.
d. 25.
e. 70.
ANS: a
50. A body is in equilibrium when
a. the sum of the forces is zero.
b. angular momentum is zero.
c. the sum of the torques is zero.
d. the sum of the torques is zero and the sum of the forces is zero.
e. the sum of the torques is zero and angular momentum is zero.
ANS: d
54. A ladder of mass m leans against a frictionless wall that exerts a normal force P on
the ladder. The coefficient of static friction between the ground and the ladder is  s . The
magnitude of the normal force the ladder exerts on the ground is
a.  s mg .
b. mg .
c. P.
d.  s P .
e.  s mg  P .
b
g
ANS: b
55. A ladder of mass m leans against a frictionless wall that exerts a normal force P on
the ladder. The coefficient of static friction between the ground and the ladder is  s . The
magnitude of the normal force P of the wall on the ladder is
P

mg
.
2 sin 
mg
P
.
2 cos 
mg
P
.
2 tan 
a. P 
b.
c.
mg
tan  .
2
 mg
P s
tan  .
2
d. P 
e.
ANS: c
66. One difference between rotational and translational motion is that in rotation
a. the angular velocity remains constant.
b. the object keeps on returning to its original angular position.
c. the axis of rotation ends up perpendicular to its original position.
d. the angular displacement remains constant.
e. the rotational kinetic energy never changes.
ANS: b
69. A sphere with a 3 kg  m 2 moment of inertia about an axis through its center has its
angular velocity changed by 4 rad/s owing to a 2 N  m torque applied about that axis for 6
s. If its initial angular velocity is 10 rad/s, the change in its rotational kinetic energy, in J,
is
a. 72.
b. 144.
c. 150.
d. 294.
e. 300.
ANS: b
72. The correct equation to use to find the velocity of the center of mass of a cylinder
after it rolls down a hill of height h from rest is
1
1
2
a. Mv CM
ICM  2f  Mgh .
,f 
b.
c.
d.
e.
2
2
1
1
2
Mv CM , f  ICM  2f  Mgh .
2
2
1
1
2
2
ICM  f  Mv CM
, f  Mgh
2
2
1
1
2
Mv CM
ICM  2f  I  Mgh.
,f 
2
2
1
1
2
Mv CM
ICM  2f  I  Mgh.
,f 
2
2
ANS: b