Name _______________________________________________________________________
Exam #2
Physics I
Fall 2007
Print your name on every page and circle section number below.
1
2
3
5
9
6
7
10
8
M/R 8-10 (Washington, DCC308)
M/R 10-12 (Yamaguchi, DCC308)
M/R 12-2 (Yamaguchi, DCC308)
M/R 2-4 (Eah, DCC318)
M/R 4-6 (Eah, DCC318)
T/F 10-12 (Malak, DCC324)
T/F 12-2 (Wetzel, DCC324)
T/F 12-2 (Adams, DCC308)
T/F 2-4 (Adams, DCC308)
Questions
Part A
Value
60
Part B
15
Part C
25
Total
100
Score
You may detach the formula sheet, but leave exam pages attached.
Cheating on this exam will result in an F in the course.
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Name _______________________________________________________________________
Part A – Multiple Choice (6 points each)
Circle the letter of the best answer.
1. A car weighing 8000 N is traveling at 12 ms along a horizontal road when the
brakes are applied. The car skids to a stop in 40 s. How much kinetic energy does
the car lose in this time?
A. 48 £ 104 J
B. 59 £ 104 J
C. 12 £ 105 J
D. 58 £ 105J
E. 48 £ 106 J
2. Suppose want to express units in terms of force (F), velocity (V) and time (T)
whenever possible. The dimensions of potential energy are then:
A. F/T
B. FVT
C. FV/T
D. F/T2
E. FV2/T2
3. A 020 kg particle moves
object. The potential energy
where is the coordinate of
it is at = 10 m, what is
A. 0
along the axis due to its interaction with a stationary
is given by () = (80 Jm2)2 + (20 Jm4)4,
the particle. If the particle has a speed of 50ms when
its speed when it is at the origin?
B. 25ms
C. 57ms
D. 79ms
E. 11ms
4. A wedge with a mass of 10 kg is at rest on a horizontal frictionless surface. A
block with a mass of 50 kg is placed on top and slides down the incline, also
starting from rest. The surface of the wedge is rough. At one instant the vertical
component of the block's velocity is 30 ms and the horizontal component is 60
ms. At that instant the velocity of the wedge is:
A. 30ms to the left
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B. 30ms to the right
C. 60ms to the right
D. 60ms to the left
E. 17ms to the right
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Name _______________________________________________________________________
5. A particle moves at constant speed in a circular path. The instantaneous velocity
and instantaneous acceleration vectors are:
A. both tangent to the circular path
B. both perpendicular to the circular path
C. perpendicular to each other
D. opposite to each other
E. none of the above
6. A block is suspended by a rope from the ceiling of a car. When the car rounds a
horizontal curve with a radius of 45 m radius at 22 ms, what angle does the rope
make with the vertical?
A. 0±
B. 25±
C. 48±
D. 65±
E. 90±
7. A wheel with a diameter of 12 m has a constant angular acceleration of 50
rads2. The tangential acceleration of a point on its rim is:
A. 50 rads2
B. 30ms2
C. 50ms2
D. 60ms2
E. 12ms2
8. The value of this product of unit vectors, k  (k  i ) , is:
A. zero
B. +1
C. -1
D. 3
E. 1.73
9. A playground merry-go-round has a radius of 30 m and a rotational inertia of
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600 kg m2. It is initially spinning at 080 rads when a 20 kg child crawls from its
center to the rim. When the child reaches the rim the angular velocity of the merrygo-round has magnitude:
A. 062 rads
B. 073 rads
C. 080 rads
D. 089 rads
E. 11 rads
10. The unit kg¢m2/s can be used for:
A. angular momentum
B. rotational kinetic energy
C. rotational inertia
D. torque
E. power
Part B – (3 points each)
Circle the letter of the best answer.
The space shuttle launches a rigid satellite upward as shown. During the launch it spins the
satellite on an axis through its center of mass then pushes it out. As it sets the satellite spinning
it fires small rockets that keep the shuttle stationary, reducing the mass of the shuttle. Neglect
the orbital motion of the system around the earth.
1. The rotational inertia of the satellite during the launch,
A. increases B. decreases C. stays positive
D. stays negative
2. The rotational kinetic energy of the satellite during the launch,
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E. none of these
Name _______________________________________________________________________
A. increases
B. decreases
C. is negative D. is upward E. none of these
3. The angular velocity of the satellite after launch is,
A. upward
B. downward C. increasing D. decreasing E. none of these
4. The angular velocity of the shuttle after launch is,
A. upward
B. downward C. increasing D. decreasing E. none of these
5. The magnitude of the angular momentum for shuttle plus satellite during launch,
A. increases B. decreases C. stays constant
E. none of these
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Name _______________________________________________________________________
Part C – Numerical Problem (25 points)
A conservative force F  ((7.0 N / m) x  8.0 N )iˆ acts on a particle that moves on an x axis. The
potential energy associated with this force is assigned a value of 26 J at x = 0. Show your work.
(a) What is the maximum potential energy for motion on the axis?
Answer: _______________J
(b) Where on the axis is the potential energy equal to zero?
Answer:_______________m
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Name _______________________________________________________________________
Formula Sheet for Homework and Exams – Page 1 of 2


U    Fcons  dx
1.
v f  v 0  a t f  t 0 
23.
2.
x f  x 0  v 0 ( t f  t 0 )  12 a ( t f  t 0 ) 2
24.
U g  m g (y  y 0 )
3.
x f  x 0  12 ( v 0  v f )( t f  t 0 )
25.
U s  12 k ( x  x 0 ) 2
4.
x f  x0  v f (t f  t0 )  12 a(t f  t0 )2
26.
27.
28.
 K   U  Wnoncons
s  r
v tangential   r
29.
a tangential   r
6.
v f  v 02  2ax f  x 0 
 

 F  Fnet  m a
7.
T
8.
a centripetal 
5.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
2
2r
v
v2
 2 r
r
a radial  a centripetal


p  mv

 
dp
 F  Fnet  d t



J   Fnet dt   p


P   pi


dP
  Fext
dt
30.
  0  t  t 0 
31.
   0  0 ( t  t 0 )  12 ( t  t 0 ) 2
32.
   0  12 (0  )( t  t 0 )
33.
   0  ( t  t 0 )  12 ( t  t 0 ) 2
 2  02  2   0 
   
35a. a  b  a b sin( )
 
a  b  a y b z  a z b y î 
35b.
a z b x  a x b z  ĵ  a x b y  a y b x k̂
34.

36.
37.
M   mi
38.
1
1
x cm   m i x i y cm   m i y i
M
M


P  M v cm
   
a  b  a b cos()  a x b x  a y b y  a z b z
 
W  Fd
 
W   F  dx
21.
K  12 m v 2  12 m (v x  v y )
22.
K f  K i  Wnet
2
39.
40.
41.
42.
43.
2
I   m i ri


2
K rot  12 I  2
 
W     d
  
  r F

 dL

  I  d t
  
l  r p


L  l i


L  I
44x. m1 v1, x ,before  m 2 v 2, x ,before  m1 v1, x ,after  m 2 v 2, x ,after
44y. m1 v1, y ,before  m 2 v 2, y ,before  m1 v1, y ,after  m 2 v 2, y,after
44z. m1 v1,z ,before  m 2 v 2,z ,before  m1 v1,z ,after  m 2 v 2,z ,after
45a. v1,f 
m1  m 2
2 m2
v1,i 
v 2 ,i
m1  m 2
m1  m 2
45b.
8
v 2,f 
2 m1
m  m1
v1,i  2
v 2 ,i
m1  m 2
m1  m 2

Formula Sheet for Homework and Exams – Page 2 of 2
46a.
46b.
47a.
47b.
48a.
48b.
49.

m m
| F | G 1 2 2
r

m m
F  G 1 2 2 r̂
r

1 | q1 || q 2 |
| F |
4  0
r2

1 q1 q 2
F
(r̂ )
4  0 r 2

1 | qi |
| Ei |
4   0 ri 2

1 qi
E
(r̂i )
4   0 ri 2


F  qE
50.
51.
52.
1 qi
4   0 ri
U  qV
 
V    E  dx
V
V
x
V
53y. E y  
y
V
53z. E z  
z

 
54. F  q v  B
mv
55. r 
qB
53x. E x  
Useful Constants
(You can use the approximate values on exams.)
Universal Gravitation Constant
G  6.67310 11 N m 2 kg 2  6.67 10 11
Electrostatic Force Constant
1
 8.987551788 10 9 N m 2 C  2  9.0 10 9
4  0
Magnetic Constant
 0  4  10 7 H m 1  1.26 10 6
Speed of Light in Vacuum
c  2.99792458 10 8 m s 1  3.0 10 8
Charge of a Proton
e  1.602176462 10 19 C  1.6 10 19
Electron-Volt Conversion Constant
1eV  1.602176462 10 19 J  1.6 10 19
Mass of a Proton
m p  1.6726215810 27 kg  1.67 10 27
Mass of an Electron
m e  9.10938188 10 31 kg  9.110 31
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