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Energy Bar Charts – In class practice
SWHS AP Physics
1.
Name:
A 100 N box is initially moving upward at 4 m/s. A man is applying a vertical force of 80 N with his hand to the
box as shown.
Draw a qualitative energy bar chart below for the earth-box system as it moves upward a distance of 1 m
with the zero point for the gravitational (potential) energy set at the initial height.
Initial system energy
KE
Eint
Final system energy
During
PEgrav PEspring Wext
Q
KE
Eint
PEgrav PEspring
Bar chart graph key
KE
Kinetic energy
Eint
Internal energy
PEgrav
PEspring
Wext
Q
Gravitational
potential energy
Spring
potential energy
Work done by
external forces
Heat added
to system
Use g = 10 m/s2
for simplicity
2.
A 40 N box initially held at rest is suddenly pulled a distance of 2 m upward by a
constant upward vertical force of 90 N. The box is attached to a fixed spring with a
stiffness of 20 N/m that is initially not stretched.
90 N
40 N
Complete the energy bar chart for the earth-box-spring system for this process.
k = 20 N/m
Initial system energy
KE
Eint
Final system energy
During
PEgrav PEspring Wext
Q
KE
Eint
PEgrav PEspring
Bar chart graph key
KE
Kinetic energy
Eint
Internal energy
PEgrav
PEspring
Wext
Q
Gravitational
potential energy
Spring
potential energy
Work done by
external forces
Heat added
to system
Use g = 10 m/s2
for simplicity
3.
A 70 N box initially at rest is pulled a distance of 4 m along a along
a rough horizontal floor by a constant horizontal force of 80 N. The
box is attached to a fixed spring with a stiffness of 20 N/m that is
initially not stretched. The maximum static frictional force is 30 N
and kinetic frictional force is 20 N between the box and surface.
Complete the energy bar chart for the surface-box-spring system
for this process.
Initial system energy
KE
Eint
k = 20 N/m
Final system energy
During
PEgrav PEspring Wext
80 N
70 N
Q
KE
Eint
PEgrav PEspring
Bar chart graph key
KE
Kinetic energy
Eint
Internal energy
PEgrav
PEspring
Wext
Q
Gravitational
potential energy
Spring
potential energy
Work done by
external forces
Heat added
to system
Use g = 10 m/s2
for simplicity
4.
A 4 kg box is dropped from a vertical height of 3 meters above an uncompressed
spring that has a spring constant of 240 N/m. The box-spring system comes to rest
momentarily when the spring is compressed by a vertical distance of 1 meter below
its initial position. (Note: the system will start oscillating after reaching this point.)
Complete the energy bar chart below for the box-earth-spring system for this
process where the zero point for the gravitational potential energy is the location
of the box when the spring has been compressed 1m (lowest point).
Initial system energy
KE
Eint
Final system energy
During
PEgrav PEspring Wext
40 N
Q
KE
Eint
PEgrav PEspring
Bar chart graph key
KE
Kinetic energy
Eint
Internal energy
PEgrav
PEspring
Wext
Q
Gravitational
potential energy
Spring
potential energy
Work done by
external forces
Heat added
to system
Use g = 10 m/s2
for simplicity
k = 240 N/m