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Problems with Solution for University Physics I | PHYS 2050, Exams of Physics
Material Type: Exam; Professor: Kaldon; Class: University Physics I; Subject: Physics; University: Western Michigan University; Term: Summer 1 2006;
Typology: Exams
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X2.17a
PHYS-205(17) (Kaldon-20619)
Name
_________S
O L U T I O
N_______
Exam 2A - 100,000 points + 20,000 WMU-Summer I 2006
points Book Title __________________________________________
06/04/2006•Rev.
State Any Assumptions You Need To Make – Show All Work – Circle Any Final Answers
Use Your Time Wisely – Work on What You Can – Be Sure to Write Down Equations
Feel Free to Ask Any Questions
2a
2b
2c
2e
EXAM 2 [FORM - A]
PHYS-2050 (KALDON-17)
SUMMER I 2006
WMU
If F=ma,
then does F²=mama?
Physics 2050 / Exam 2 [Form-A]
Summer 2006
Page 2
(b) The weight of the loaded elevator at rest is 10,500 N. With what force must the guy pull on the rope? Assume all the cable tensions are the same. a rope. Draw the Free Body Diagram of the loaded elevator car at rest. 1.) (a) A cargo elevator at an open mine shaft is being pulled on by means of Problem One – “The One That Goes Up and Down” (35,000 points)
F
T
w
T
w
T
w
N
N
y
0
1
1
1
,
.
(c) If the elevator is to be lowered at 1.11 m/s², with what force must the guy pull on the rope?
w
mg
m
w g
N
m
s
kg
F
T
w
ma
T
w
ma
T
w
ma
N
kg
m
s
N
y
y
y
y
2
1
1
1
2
,
.
/
.
,
.
.
/
b
gc
h
(d) If the elevator is to be lowered at 1.11 m/s, with what force must the guy pull on the rope?
F
T
w
T
w
T
w
N
N
y
0
1
1
1
,
.
Same answer as (b)!
Physics 2050 / Exam 2 [Form-A]
Summer 2006
Page 3
(e) If there was
no
air resistance, then the elevator would be in free fall the whole way. Use conservation
of energy to find the speed of the elevator after it has fallen 933 meters.
NOTE: Missing part of the sentence here! If the cable breaks and there was
no
air resistance…
mgh
mv
mgh
mv
mgh
mv
gh
v
v
gh
v
gh
m
s
m
m
s
1
21
1 2
2
21
22
1
21
22
1
21
22
2 2
1
2
1
2
.
/
.
/
c
hb
g
NOTE: OK if student starts with v
1
= -1.11 m/s from part (d) rather than from rest…
mgh
mv
mgh
mv
h
mgh
mv
mv
gh
v
v
v
gh
v
v
gh
v
m
s
m
m
s
m
s
1
21
12
2
1
2
2 2
2
1
21
12
21
22
1
21
1 2
21
22
2 2
1
1 2
2
1
1 2
2
2
0
2
2 2 9 81
933
111
135 3
;
.
/
.
/
.
/
c
hb
g b
g
Physics 2050 / Exam 2 [Form-A]
Summer 2006
Page 4
2.) Problem Two – “The One With The Star Problems” (30,000 points)
(a) A small red ball (mass
m = 0.200 kg
) is moving to the right with a speed 10.0 m/s at time zero.
It is attached to an elastic cord which applies a force to the left with
F
C x i
elastic
. Find the distance
d
it takes the ball to come to a stop, where
x
0
= 0
and the coefficient of the cord is
C = 5.00 N/m
, using
work and energy.
K
mv
kg
m
s
J
W
F ds F dx
Cx dx
C
x dx
C
x
Cd
W
K
K
K
J
Cd
J
Cd
d
J
C
J
N
m
d
J
N
m
m
x
d
d
d
d
f
i
z
z
z
z
21
2
21
2
0
0
0
2
0
2
2
2
2
.
.
/
.
.
.
.
.
.
/
.
.
/
.
b
gb
g
b
g
b
g
An object of mass
m = 12.0 kg
begins its motion with the following equation. All other constants are
zero.
(b) Find the force,
F
, acting on this object at time
t = 1.00 sec
.
a
d
x
d t
m
s
t
F
ma
kg
m
s
t
kg m
s
t
F t
kg m
s
N
2
2
6
4
6
4
6
4
6
4
(
.
/
)
.
(
.
/
)
(
.
/
)
(
.
sec)
(
.
/
)
.
sec
.
b g b g d x
d t
m
s
t
2
2
6
4
12 0
(
.
/
)
Physics 2050 / Exam 2 [Form-A]
Summer 2006
Page 5
(c) A block of mass
m = 1.00 kg
starts out at rest at a position
x
0
= 4.00 meters
, and moves with a force
F
t
t
x
N
s
( )
.
2
2
d
i
. Find the position
x
of the block after 5.00 seconds.
Assume any other constants
are zero.
F
t
t
F
ma
a
F
m
t
kg
m
s
t
d td x
v
d x d t
d td x
dt
m
s
t
dt
m
s
t
C
C
x
d x d t
dt
m
s
t dt
m s t C C x m
m
s
t
x
sN
x
x
x
x
N
s
x
( )
.
.
.
.
/
.
/
.
/
(
)
.
/
.
/
(
.
)
.
/
z
z
z
z
0
2
2 2
2
4
2
2
2
2
2
4
2
31
4
3
31
4
3
1
3 4
4
4
0
4
4
d
i
d
i
c
h
c
h
c
h
c
h
c
h
c
h
.
(
.
sec)
.
/
.
sec
.
00
4
4
m
x t
m
s
m
m
c
hb
g
carts ( (d) Jerry is putting grocery carts away at Meijer. He takes one of the
m = 10.2 kg
) and gives it a shove so it is traveling at 4.75 m/s.
just sitting there. Find the speedIt crashes into and sticks with a group of five grocery carts that were
V
of the new group of grocery carts.
p
p
m v
m v
m v
m v
m v
m v
m m m m m m
m V
mv
mV
V
mv
m v m s m s
before
after
1 1 2 2 3 3 4 4 5 5 6 6 1 2 2 3 4 5 6
0
b
g
.
/
.
/
Physics 2050 / Exam 2 [Form-A]
Summer 2006
Page 6
(e) An object of mass 1.00 kg has a motion that follows the following equations. Find the magnitude
K
of the kinetic energy of the object at time
t = 0
and
t = 10.0 seconds
. Then find how much Work was
done to move the object – It Won’t Take Calculus for this last bit.
x t
m
m
s
m
s
( )
.
.
/
.
/
2
3
t
t
2
3
x t
m
m
s
m
s
v
d td x
d
d t
m
m
s
m
s
m
s
m
s
m
s
m
s
v tv
m
s
m
s
m
s
K K
mv
i
f
( )
.
.
/
.
/
.
.
/
.
/
(.
/
)
(5.
/
)
(. / ) (. / )
( ( )
. sec)
(
.
/
)
. sec)
(
.
/
)
. sec)
.
/
0
00
0
0
0
2
3
2
3
2
3
2
3
2
3
21
2
t
t
t
t
t
t
t
t
(
(
2
3
2
3
2
2
2
c
h
21
2
0
.
.
/
,
,
,
kg
m
s
J
W K K K J J
f
i
b
gb
g
Physics 2050 / Exam 2 [Form-A]
Summer 2006
Page 7
3.) Frida has to get a refrigerator ( Problem Three – “The One With All The Angles” (35,000 points)
m = 135 kg
) loaded onto a truck, using a
speed.find (a) the force needed to push the refrigerator up the ramp at a constantramp that is angled at 22°. If the refrigerator glides on frictionless rollers,
F
F
w
F
w
mg
kg
m
s
N
x
x
x
1
1
2
0
. sin
/
sin
.
b
gc
h
(b) The ramp is 1.50 m tall, while the angled part is 4.00 m long. Show that the work to raise the
refrigerator 1.50 m is the same as the work in pushing the refrigerator up the slope without friction.
W
mgh
kg
m
s
m
J
W
Fd
N
m
J
2
b
gc
hb
g
b
gb
g
.
/
.
.
.
(c) If the elevator did
not
have the rollers, that it could sit on the ramp and be held in place by static
friction without being held by Frida. Find the
minimum
coefficient of static friction,
s
.
F
F
w
F
F
w
F
F
w
w
mg
mg
mg
mg
y
N
y
x
f
s
x
f
s s N s y x
s s
0
0
, ,max
, ,max
cos
sin
sin
cos
tan
tan
.
Physics 2050 / Exam 2 [Form-A]
Summer 2006
Page 8
the maximum force Frida can push the stopped refrigerator without having it move up the ramp?(d) The actual coefficients of friction between the refrigerator and the ramp are 0.857 and 0.657. What is
F
F
w
F
w
F
F
F
w
F
F
w
w
w
mg
mg
mg
kg
m
s
N
y
N
y
N
y
x
f
s
x
f
s
x
s
y
x
s
s
0
0
1
1
2
;
cos
sin
cos
sin
.
/
.
cos
sin
, ,max
, ,max
b
g
b
gc
h b
g
c
h
constant speed with friction? (e) What is the force that Frida needs to apply to the refrigerator to get it up the ramp if is sliding at a
F
F
w
F
w
F
F
F
w
F
F
w
w
w
mg
mg
mg
kg
m
s
N
y
N
y
N
y
x
f
k
x
f
k
x
k
y
x
k
k
0
0
1
1
2
;
cos
sin
cos
sin
.
/
.
cos
sin
,
,
b
g
b
gc
h b
g
c
h