PHY 206 Fall 2001 Exam #2
15 point problems. Be certain to show all of your work.
1.
A mass m2 = 2.0 kg rests on a table as shown in Fig. 1. The
coefficients of friction between m2 and the table are s = 0.3
and k = 0.25. Mass m2 is attached by strings to masses m1
= 3.0 kg and m3 = 5.0 kg as shown. The system is initially
held at rest. After it is released, what is the acceleration of
m2?
2.
A coin is placed on a turntable at a distance of 16 cm from
the center. The turntable rotates with a period of 1.46 s and
the coin remains on the turntable without slipping.
a)Draw a free-body diagram, carefully labeling all
forces acting on the coin.
b)What is the minimum coefficient of friction necessary to keep the coin from slipping?
10 point problems.
3.
The object shown in Fig. 2 has a mass of 3.45 kg and
is pulled up the slope, which is 36 m long. The
height is 3.0 m. There is no friction and the
acceleration is constant. At the bottom of the ramp,
the speed is 3.5 m/s; at the top, the speed is 5.5 m/s.
What is the power needed by the motor that pulls the
object up the ramp? (Hint: You will need to find the
acceleration and the time needed to get to the top.)
4.
A vertical rope is attached to an object that has a
mass of 40.0 kg and is at rest.
a) Draw a free-body diagram showing the relevant forces on the object.
b) Find tension in the rope needed to give the object an upward speed of 3.5 m/s in 0.70 s.
5 point questions.
5.
Which of the following statements includes all the essential elements of Newton’s First Law?
a) A body at rest persists in its state of rest unless acted on a by a non-zero net external force.
b) A body persists in its state of rest or of uniform motion in a straight line as long as thenet external
force remains constant.
c) For every action there is an equal and opposite reaction
d) A body persists in its state of rest or of uniform motion in a straight line unless acted on by a nonzero net external force
e) The acceleration of a body is proportional to the net external force acting on it and to the mass of
the body.
6.
A body moves with constant speed in a straight line. Which of the following statements must be true?
a) No force acts on the body.
b) A single constant force acts on the body in the direction of motion.
c) A single constant force acts on the body in the direction opposite to the motion.
d) A net force of zero acts on the body.
e) A constant net force acts on the body in the direction of motion.
7.
An 80-kg man on ice skates pushes a 40-kg boy, also on skates, with a force of 100 N. The force
exerted by the boy on the man is
a) 200 N
b) 100 N
c) 50 N
d) 40 N
e) zero unless the boy pushes back
8.
A particle moving with uniform circular motion has a period of 0.24 s and a speed of 4.2 m/s. The
radius of the path of the particle is
a) 16 cm
b) 2.6 cm
c) 1.0 m
d) 0.062 cm
e) 1.4 cm
9.
A worker pulls horizontally on a rope that is attached to a 10-kg create resting on a rough floor. The
coefficients of friction are s = 0.5 and k = 0.3. The worker pulls with a force of 40 N. The
frictional force exerted by the surface is
a) 30 N
b) 50 N
c) 10 N
d) 100 N
e) 40 N
10. Which free-body diagram best represents the forces
acting on the student sliding down the slightly rough
inclined plane shown in Fig. 3 ?
11. An object traveling in a circle at constant speed
a) is moving with constant velocity
b) may be slowing down or picking up speed
c) experiences no acceleration
d) experiences an acceleration toward the center of the
circle
e) is described by none of the above statements
12. The work expended to accelerate a car from 0 to 30 m/s
a) is more than that required to accelerate it from 30
m/s to 60 m/s
b) is equal to that required to accelerate it from 30 m/s to 60 m/s
c) is less than that required to accelerate it from 30 m/s to 60 m/s
d) can be described by any of the preceding, depending on the time taken
e) is described by none of these statements
13. A 5-kg object undergoes a displacement s  2iˆ  3 ˆj . During the displacement, a constant force
F  4iˆ  2 ˆj acts on the object. All values are given in SI units. The work done by the force on this
object is
a) 8 J
b) –6 J
c) 2 J
e) –2 J
d) 14 J
14. A 5200-kg cable car is pulled a distance 0f 360 m up a hill inclined at 12 from the horizontal. The
change in potential energy of the car is
a) 1.8107 J
b) 1.2107 J
c) 3.8106 J
d) 6.0107 J e) 3.8105 J
Possibly useful equations:
dx
x
v
v(t ) 
vav 
aav 
dt
t
t
x  x0  v0 x t 
1
a xt
2
2
y  y0  v0 y t 
1
a yt
2
2
g = 9.81m/s2 v
v  v0 x  a x t
x
v
av

r
t
2
2
 v  2a x x
x
0x
2
2
v  v0 y  a y t v  v  2 a y y
y
0y
y
W  Fx x
W  K
W  U
U  U 0  mgy
K
1 2
mv
2
a
v (t ) 
a
dt
F  F
net
T
A  B  AB cos
m1  m2
g
m1  m2
dr
T
av

 ma
2 r
v
ac 
W  F  s
2m1m2 g
m1  m2
v
a (t ) 
t
dv
dt
fs,max = sFn
fk = kFn
v2
r
P
dW
 F v
dt