Q6.2.a: A ball whose mass is 2 kg travels at a velocity of
< 0, –3, 4> m/s.
1) < 0, –6, 8 > J
2) < 0, –3, 4 > J
3) 2 J
4) 10 J
5) 25 J
What is the kinetic energy of the ball?
Q6.2.aa: A ball whose mass is 2 kg travels at a velocity of
< 0, –3, 4> m/s.
1) 0 J
2) 25 J
3) 6e8 J
4) 9e16 J
5) 1.8e17 J
What is the rest energy of the ball?
Q6.2.b: A ball whose mass is 2 kg travels at a velocity of
< 0, –3, 4> m/s.
What is the total energy of the ball?
(
)
Erest = mc 2 = ( 2 ) 3 ´108
2
1) 0 J
2) 25 J
3) 6e8 J
4) 9e16 J
5) 1.8e17 J
= 18 ´1016 J
Q6.2.c:
Consider an electron (mass 9e-31 kg) moving with speed v = 0.9c. What is its rest
energy?
(
)(
Erest = mc 2 = 9.1´10 -31 3 ´108
)
2
= 0.819 ´10 -13 J
Q6.2.d:
Consider an electron (mass 9e-31 kg) moving with speed v = 0.9c. What is its total
(particle) energy?
E=
1
2
1-
v
c2
mc 2 =
(
)(
= 2.294 9.1 ´ 10 -31 3 ´ 10 8
-31
2
)
1) 7.3e-31 J
2) 8.1e-14 J
3) 1.05e-13 J
4) 1.86e-13 J
5) 2.7e8 m/s
( 9.1 ´ 10 )( 3 ´ 10 )
1
1- ( 0.9 )
1) 7.3e-31 J
2) 8.1e-14 J
3) 1.05e-13 J
4) 1.86e-13 J
5) 2.7e8 m/s
2
8 2
= 1.88 ´ 10 -13 J
Q6.2.e:
Consider an electron (mass 9e-31 kg) moving with speed v = 0.9c. Its rest energy is
0.81e-13 J, and its (total) particle energy is 1.86e-13 J. What is its kinetic energy?
1) 7.3e-31 J
2) 3.28e-14 J
3) 8.1e-14 J
4) 1.06e-13 J
5) 1.86e-13 J
K = E - Erest = 1.88 ´10 -13 J - 0.819 ´10 -13 J = 1.06 ´10 -13 J
Chapter 6 Clickers
1
Q6.3.a: On a space station, you pushed a box that was initially floating at rest at
location < 0, 0, 10 > m to location < 0, 0, 14 > m, applying a force < 0, 0, 5 > N. How
much work did you do on the box?
1) W = 20 J
2) W = 50 J
3) W = 70 J
4) W = 140 J
5) Not enough information
Q6.3.b: You did 20 J of work on the box. What happened?
1) The box slowed down.
2) The box speeded up.
3) The box moved at constant speed.
Q6.3.c: You apply a force of < 0, 0, 5 > N to a box for 3 seconds. How much work did you do on the
box?
1) W = 15 J
2) W = 5 J
3) W = 3 J
4) W = 5/3 J
5) Not enough information.
Q6.3.d
A figure skater slides in the –x direction along the ice, toward her partner. When she gets close he pushes on her
in the +x direction, to slow her down. Does he do positive, negative, or zero work?
1) positive
2) negative
3) zero
Dr
F
Q6.3.e
A fancart moves in the –x direction. The fan is on, and the force on the cart by the air is also in the –x
direction. Is the work done by the air positive, negative, or zero?
1) positive
2) negative
3) zero
Dr
F
Q6.3.f
A skater on a skateboard coasts in the +x direction. He is about to run into his friend, so she pushes him in the –x
direction, to slow him down. What is the sign of the work done by the friend?
Dr
1) positive
2) negative
3) zero
F
Q6.3.g: A tennis ball is moving in the –y direction. You hit it downward with a
tennis racket. During the time your racket is in contact with the ball, do you do
positive, negative, or zero work on the ball?
Dr
1) positive
2) negative
3) zero
F
Chapter 6 Clickers
2
The diagram shows a force acting on an object and the displacement of the
object while the force acts.
1) positive
2) negative
3) zero
Q6.3.h
You move an object from
< 3, 7, 4 > m to < 2, 10, 12 > m, applying a force < 10, –20, 30 > N
1) 10 J
2) 170 J
3) < -10, -60, 240 > J
4) < 30, -140, 120 > J
5)  10 2   60 2  2402 J
How much work do you do?
Q6.3.i
You drop a ball of mass m at a height h above the ground. The ball falls, speeding up, bounces
off the floor, and goes upward, slowing down, until it is once again at the location where you
released it (height h).
Initial state: Just after release
Final state: Ball back at original location
Q6.5.a: An isolated neutron decays:
Initial: Neutron at rest
Final:
How much work was done by the Earth on the ball?
1) mgh
2) –mgh
3) 2*mgh
4) –2*mgh
5) 0
n  p  e   

p  , e , and  far from each other
1) The sum of the rest energies of the products equals the
rest energy of the neutron
2) The sum of the kinetic energies of the products equals the rest
energy of the neutron
3) The sum of the rest energies and kinetic energies of the products
equals the rest energy of the neutron
4) The sum of the kinetic energies of the products equals the
kinetic energy of the neutron
Q6.5.b: An isolated neutron decays: n  p   e   
Initial: Neutron at rest
Final:
System: All particles
p , e

, and
 far from each other
Energy principle: Ef = Ei + W
What quantities are included in the initial energy Ei?
A: Kn
C: Ke
E: mnc2
G: mec2
B: Kp
D: K
F: mpc2
H: mc2
1) A 2) A, E
3) A, B, C, D
4) E, F, G, H
Q6.5.c: An isolated neutron decays: n  p   e   
Initial: Neutron at rest
Final:
System: All particles
p , e

5) A, F, G, H
, and
 far from each other
Energy principle: Ef = Ei + W
What quantities are included in the final energy Ef?
A: Kn
Chapter 6 Clickers
C: Ke
E: mnc2
G: mec2
3
B: Kp
1) A, C, E, G
D: K
2) B, C, D, F, G, H
F: mpc2
H: mc2
3) A, E 4) B, C, D 5) E, F, G
Q6.7.a:
You push a crate out of a carpeted room and along a tiled hallway.
While on the carpet you exert a force of 30 N and the crate moves 2 m.
While on the tile you exert a force of 12 N and the crate moves 8 m.
How much work do you do?
1) 210 J
2) 180 J
3) 156 J
4) 105 J
5) 42 J
6) We need to know the mass of the crate.
Q6.7.b
A horizontal spring has stiffness 100 N/m. A block is pressed against the spring, compressing the
spring 0.2 m, and then released. When the spring has reached its relaxed length, how much work
will it have done on the block?
1) 20 J
2) 4 J
3) 2 J
4) 0 J
5) We need to know the mass of the block
Q6.8.a
A thrown ball heads straight up.
SYSTEM: Ball
What is the work done by the surroundings?
1) 0
2) mgy
3) –mgy
4) something else
Q6.8.b
A thrown ball heads straight up.
SYSTEM: Ball + Earth
What is the work done by the surroundings?
1) 0
2) mgy
3) –mgy
4) something else
Q6.8.c
Chapter 6 Clickers
4
A thrown ball heads straight up.
SYSTEM: Ball + Earth
How did the kinetic energy of the system change?
1) K > 0
2) K = 0
3) K < 0
Q6.8.d
A ball of mass 0.1 kg is dropped from rest near the Earth.
The ball travels downward 2 m, speeding up.
What is the work done by the surroundings?
1) 0
2) + 1.96 J
3) – 1.96 J
SYSTEM: Ball
Q6.8.e
A ball of mass 0.1 kg is dropped from rest near the Earth.
The ball travels downward 2 m, speeding up.
What is the work done by the surroundings?
1) 0
2) + 1.96 J
3) – 1.96 J
SYSTEM: Ball + Earth
Q6.8.f
A ball of mass 0.1 kg is dropped from rest near the Earth.
The ball travels downward 2 m, speeding up.
SYSTEM: Ball + Earth
Work done by surroundings: 0
However, did the kinetic energy of the Ball + Earth system change?
1) K increased
2) K decreased
3) K did not change
Q6.9.a For the system of Ball + Earth, K > 0 but W = 0. We have a problem...Q6.9.a
A spacecraft travels from near the Earth toward the Moon. How many gravitational
potential energy terms Ug are there in the Energy Principle?
System: Earth, Moon, spacecraft
1) 1
2) 2
3) 3
4) 6
5) 0
Q6.11.a:
Which of the following graphs of U vs r represents the
gravitational potential energy, U = –GMm/r? 1
Chapter 6 Clickers
5
Q6.11.b: In which graph does the cyan line correctly represent the
sum of kinetic energy plus potential energy?
1) A
Chapter 6 Clickers
2) B
3) C
6
Q6.12.a
A comet orbits a star in a strongly elliptical orbit. The comet and star are far
from other massive objects.
System: comet + star
The system has:
1) kinetic energy
2) kinetic energy and rest energy
3) kinetic energy, rest energy, and potential energy
Q6.12.b
System: comet + star
1)
2)
3)
4)
5)
As the comet travels away from the star, how does the kinetic
energy and potential energy of the system change?
K
increase
increase
decrease
decrease
no change
U
decrease
increase
increase
decrease
no change
Q6.12.c: A robot spacecraft leaves an asteroid. SYSTEM: craft + asteroid
Which quantities are the same in the initial state and the final state
(that is, which quantities do not change significantly, for this system)?
1) rest energy of asteroid, rest energy of spacecraft
2) rest energy of asteroid, rest energy of spacecraft, and
kinetic energy of asteroid
3) rest energy of asteroid, rest energy of spacecraft, and
gravitational potential energy
4) rest energy of asteroid, rest energy of spacecraft, and
kinetic energy of asteroid, and gravitational potential energy
Q6.12.d:
The system is a comet and a star. In which case(s) will the
comet escape from the star and never return?
1) A
2) B
3) C
4) A,B
5) B,C
6) A,B,C
Q6.14.a
Jack pulls to the left on a positive charge, while Jill pulls to the right on a
negative charge.
System: both charges
Chapter 6 Clickers
Which forces are external?
1) F1 and F2
2) F2 and F3
3) F3 and F4
4) F1 and F4
7
Q6.14.b
The charges are displaced, then remain at rest.
System: both charges
The work done by external forces was:
1) positive
2) negative
3) zero
4) need more information
Q6.14.c
System: both charges
Initial state: charges at rest
Final state: charges at rest, farther apart
The positive work done by external forces:
1) increased K of the system
2) decreased K of the system
3) did not change K of the system
Q6.14.d
y-axis: energy; x-axis: separation
Which graph correctly shows U for a proton and an electron?
5: none of the above
Q6.14.e
y-axis: energy; x-axis: separation
Which graph correctly shows U for two interacting protons?
5: none of the above
Q6.14.f Two electrons, initially far apart, heading toward each other.
Same initial speed v. How close do they get before stopping?
Which terms are NOT zero?
1) K1f
K1f + K2f + Uf = K1i + K2i + Ui + W
, K2f
2) Uf
3) K1i
, K2i
Q6.14.g
Two electrons, initially far apart, heading toward each other.
By applying the energy principle we found that:
Uf = K1,i + K2,i
Chapter 6 Clickers
4) Ui
5)K1f , K2f, Ui
6) K1i , K2i, Uf
Which term contains the distance
of closest approach?
1) Uel,f
2) K1,i
8
3)K2,i
4) None of the above
Q6.14.h
y-axis: energy; x-axis: separation
Which graph shows K, U, and K+U for the two interacting electrons? 4
5: none of the above
Q6.17.a: alpha + carbon => oxygen + photon
What is the minimum initial kinetic energy of the alpha particle?
mOc2 + KO + E = mc2 + mCc2 + K + Kc + Ui
1
2
3
4
5
6
7
8
Which term contains the unknown?
Q6.17.b: alpha + carbon => alpha + carbon just barely touching each other
What is the minimum initial kinetic energy of the alpha particle?
Uf = K + Kc
1
2
3
Which term contains the unknown?
Chapter 6 Clickers
9