Transcript MC Practice #2 Ekina energy starter

Chapter 6 Clickers
Work and Energy
Prepared by
Dedra Demaree,
Georgetown University
© 2014 Pearson Education, Inc.
Which of the following statements is true about
external force and displacement?
a) If an external force is applied in the direction of an
object's displacement, the object gains more
potential to do something.
b) If an external force is applied against the direction
of an object's displacement, the object's potential
to do something decreases.
c) If an external force is applied perpendicular to an
object's displacement, the object's potential to do
something is unchanged.
d) All of the above are correct.
© 2014 Pearson Education, Inc.
Which of the following statements is true about
external force and displacement?
a) If an external force is applied in the direction of an
object's displacement, the object gains more
potential to do something.
b) If an external force is applied against the direction
of an object's displacement, the object's potential
to do something decreases.
c) If an external force is applied perpendicular to an
object's displacement, the object's potential to do
something is unchanged.
d) All of the above are correct.
© 2014 Pearson Education, Inc.
The two bar charts represent a falling acorn. Which
statement below is NOT correct?
Representation A: [make a bar chart with 0 initial energy, -Ug and +K
final energy]
Representation B: [make a bar chart with 0 initial energy, +work done,
and +K final energy]
a) In representation A, Earth was in the system; in representation B, it
was not.
b) In representation A, the origin for the y-axis was at the initial
position of the acorn.
c) In representation B, the person who drew the bar chart forgot to
include the potential energy of gravity.
d) More than one representation can be correct for this situation.
© 2014 Pearson Education, Inc.
The two bar charts represent a falling acorn. Which
statement below is NOT correct?
Representation A: [make a bar chart with 0 initial energy, -Ug and +K
final energy]
Representation B: [make a bar chart with 0 initial energy, +work done,
and +K final energy]
a) In representation A, Earth was in the system; in representation B, it
was not.
b) In representation A, the origin for the y-axis was at the initial
position of the acorn.
c) In representation B, the person who drew the bar chart forgot
to include the potential energy of gravity.
d) More than one representation can be correct for this situation.
© 2014 Pearson Education, Inc.
What can we NOT conclude from the following
graphed data?
A graph of the stretch of springs 1
and 2 when the same force is
exerted on each spring.
a)
b)
c)
d)
Force = mx + 0, where m is the
slope.
Spring 2 stretches farther than
spring 1 when the same amount
of force is applied.
If 2 N of force is exerted on
spring 1, it is stretched by 0.1 m.
All of the above are correct.
© 2014 Pearson Education, Inc.
What can we NOT conclude from the following
graphed data?
A graph of the stretch of springs 1
and 2 when the same force is
exerted on each spring.
a)
b)
c)
d)
Force = mx + 0, where m is the
slope.
Spring 2 stretches farther than
spring 1 when the same
amount of force is applied.
If 2 N of force is exerted on
spring 1, it is stretched by 0.1 m.
All of the above are correct.
© 2014 Pearson Education, Inc.
A pole vaulter crosses a bar high above a cushion
below. Which equation is NOT correct for the initial
situation when the vaulter is at the highest point and
the final situation when the vaulter has sunk a
distance x into the cushion (modeled as a spring)?
a)
b)
c)
d)
mgh = -mgx + (1/2)kx2
mg(h + x) = (1/2)kx2
0 = -mg(h + x) + (1/2)kx2
All of the above are correct.
© 2014 Pearson Education, Inc.
A pole vaulter crosses a bar high above a cushion
below. Which equation is NOT correct for the initial
situation when the vaulter is at the highest point and
the final situation when the vaulter has sunk a
distance x into the cushion (modeled as a spring)?
a)
b)
c)
d)
mgh = -mgx + (1/2)kx2
mg(h + x) = (1/2)kx2
0 = -mg(h + x) + (1/2)kx2
All of the above are correct.
© 2014 Pearson Education, Inc.
You load an arrow into a bow and pull the bowstring
back 0.50 m. The bow has a spring constant
k = 2000 N/m. What is the potential energy of the
bowstring?
a)
b)
c)
d)
e)
125 J
250 J
500 J
1000 J
Impossible to determine without knowing the mass
© 2014 Pearson Education, Inc.
You load an arrow into a bow and pull the bowstring
back 0.50 m. The bow has a spring constant
k = 2000 N/m. What is the potential energy of the
bowstring?
a)
b)
c)
d)
e)
125 J
250 J
500 J
1000 J
Impossible to determine without knowing the mass
© 2014 Pearson Education, Inc.
Which of the following statements is NOT correct?
a) If you include both the work done by friction and
the internal energy evidenced by the surface's
heating, you are overcounting.
b) It is best to include the surface in your system so
there is no work done by friction.
c) Our model for friction leads to energy (evidenced
by heat) that we cannot incorporate through work
done by friction.
d) All of the above are correct.
© 2014 Pearson Education, Inc.
Which of the following statements is NOT correct?
a) If you include both the work done by friction and
the internal energy evidenced by the surface's
heating, you are overcounting.
b) It is best to include the surface in your system so
there is no work done by friction.
c) Our model for friction leads to energy (evidenced
by heat) that we cannot incorporate through work
done by friction.
d) All of the above are correct.
© 2014 Pearson Education, Inc.
Which of the following statements is NOT correct
about work-energy bar charts?
a) A work-energy bar chart helps to organize the
energies involved in a process.
b) A work-energy bar chart can be translated directly
into an equation.
c) A work-energy bar chart represents the constancy
of energy.
d) All of the above are correct.
© 2014 Pearson Education, Inc.
Which of the following statements is NOT correct
about work-energy bar charts?
a) A work-energy bar chart helps to organize the
energies involved in a process.
b) A work-energy bar chart can be translated directly
into an equation.
c) A work-energy bar chart represents the constancy
of energy.
d) All of the above are correct.
© 2014 Pearson Education, Inc.
For the example of an elevator slowing to a stop, to
find the constant tension force that the cable exerts
on the elevator, which of the following statements is
NOT correct?
a) This problem can be solved by finding the work
that the rope tension force exerts on the elevator.
b) This problem can be solved using Newton's second
law and kinematics.
c) Both of the above are correct.
© 2014 Pearson Education, Inc.
For the example of an elevator slowing to a stop, to
find the constant tension force that the cable exerts
on the elevator, which of the following statements is
NOT correct?
a) This problem can be solved by finding the work
that the rope tension force exerts on the elevator.
b) This problem can be solved using Newton's second
law and kinematics.
c) Both of the above are correct.
© 2014 Pearson Education, Inc.
For the example of an elevator slowing to a stop, to
find the constant tension force that the cable exerts
on the elevator, which of the following equations is
NOT helpful?
a)
b) vf2 = vi2 + 2a(yf-yi)
c) Both of the above are correct.
© 2014 Pearson Education, Inc.
For the example of an elevator slowing to a stop, to
find the constant tension force that the cable exerts
on the elevator, which of the following equations is
NOT helpful?
a)
b) vf2 = vi2 + 2a(yf-yi)
c) Both of the above are correct.
© 2014 Pearson Education, Inc.
To launch a 100-kg human so that he leaves a
cannon moving at a speed of 4 m/s, you need a
spring with an appropriate spring constant. This
spring will be compressed 2.0 m from its natural
length to launch the person. Which spring constant
do you need?
a)
b)
c)
d)
200 N/m
400 N/m
800 N/m
1600 N/m
© 2014 Pearson Education, Inc.
To launch a 100-kg human so that he leaves a
cannon moving at a speed of 4 m/s, you need a
spring with an appropriate spring constant. This
spring will be compressed 2.0 m from its natural
length to launch the person. Which spring constant
do you need?
a)
b)
c)
d)
200 N/m
400 N/m
800 N/m
1600 N/m
© 2014 Pearson Education, Inc.
Which of the following is always true about
collisions?
a) Energy is conserved in a system that includes only
the colliding objects.
b) Linear momentum is conserved in a system that
includes only one of the colliding objects.
c) Mass is conserved for a system that includes the
colliding objects.
d) All of the above are correct.
© 2014 Pearson Education, Inc.
Which of the following is always true about
collisions?
a) Energy is conserved in a system that includes only
the colliding objects.
b) Linear momentum is conserved in a system that
includes only one of the colliding objects.
c) Mass is conserved for a system that includes
the colliding objects.
d) All of the above are correct.
© 2014 Pearson Education, Inc.
Xueli is doing a dead lift. She lifts a 10-kg barbell
from the floor to just below her waist (a vertical
distance of 0.50 m) in 1 s. What is the power in this
process? (Assume g to be 10 m/s2.)
a)
b)
c)
d)
10 W
50 W
100 W
Impossible to determine from the given information
© 2014 Pearson Education, Inc.
Xueli is doing a dead lift. She lifts a 10-kg barbell
from the floor to just below her waist (a vertical
distance of 0.50 m) in 1 s. What is the power in this
process? (Assume g to be 10 m/s2.)
a)
b)
c)
d)
10 W
50 W
100 W
Impossible to determine from the given information
© 2014 Pearson Education, Inc.
Jim (mass = 100 kg) rollerblades on a smooth
horizontal floor at a constant speed of 2.0 m/s for a
distance of 5.0 m in 5.0 s. What is the power in this
process? (Assume that g is10 m/s2.)
a)
b)
c)
d)
0W
40 W
1000 W
Impossible to determine with the given information
© 2014 Pearson Education, Inc.
Jim (mass = 100 kg) rollerblades on a smooth
horizontal floor at a constant speed of 2.0 m/s for a
distance of 5.0 m in 5.0 s. What is the power in this
process? (Assume that g is10 m/s2.)
a)
b)
c)
d)
0W
40 W
1000 W
Impossible to determine with the given information
© 2014 Pearson Education, Inc.
Unit analysis on the following equation shows that
"G" must have which units?
a)
b)
c)
d)
Nm/kg
Nm2/kg
Nm/kg2
Nm2/kg2
© 2014 Pearson Education, Inc.
Unit analysis on the following equation shows that
"G" must have which units?
a)
b)
c)
d)
Nm/kg
Nm2/kg
Nm/kg2
Nm2/kg2
© 2014 Pearson Education, Inc.