OAT Practice
th
8 Grade Science
Physical
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A teacher places a ribbon of magnesium on a wire and suspends it
in a flask. She then seals the flask and runs electricity through the
wire to ignite the magnesium. After the magnesium is completely
burned, a student
notices a white powder
in the bottom of the
flask. The mass of the
flask system (the flask
and its contents) is
determined before and
after the magnesium is
ignited.
1) Which statement correctly compares the mass of the
flask system before the magnesium burned with the
mass of the flask system after the magnesium
burned?
A. The mass of the flask system before burning is
greater than the mass of the flask system after
burning.
B. The mass of the flask system before burning is less
than the mass of the flask system after burning.
C. The mass of the flask system before burning is the
same as the mass of the flask system after burning.
D. The mass of the flask system before burning is not
related to the mass of the flask system after burning.
1)
A.
B.
C.
D.
Which statement correctly compares the mass of the flask system
before the magnesium burned with the mass of the flask system after
the magnesium burned?
The mass of the flask system before burning is greater than the mass
of the flask system after burning.
If a student chooses A, he or she may have thought that mass was lost
during the burning of the magnesium ribbon. But the mass of the
magnesium ribbon and gases are the same as the mass of the white
powder and gases in the flask. So, the mass of the flask system before
burning is the same as the mass of the flask system after burning.
The mass of the flask system before burning is less than the mass of
the flask system after burning.
If a student chooses B, he or she may have thought that there was
more mass after the magnesium ribbon burned in the flask. The
stopper stayed in the flask during the whole burning process, so
nothing could be added to the flask system. So, the mass did not go
up after the ribbon burned.
The mass of the flask system before burning is the same as the
mass of the flask system after burning.
This is the correct answer. The law of conservation of matter says
that the matter of a closed system will stay the same because the
small particles that compose this matter cannot be created or
destroyed, but can change form. Because the stopper stays in the
flask at all times, this system is considered closed. The magnesium
combined with the oxygen (one of the gases in the air in the sealed
container) to create a new compound.
The mass of the flask system before burning is not related to the mass
of the flask system after burning.
If a student chooses D, he or she may have thought that the masses
are not related because of the burning. But the masses of the two
flask systems are related because they contain the same amount of
small particles that composed (made up) the matter in the flask
system before and after burning. In a closed system, like a stoppered
flask, mass is always conserved (stays the same).
Density Experiment
Two graduated cylinders
pictured can hold the
same amount of water and
use the same scale. A
student measures the
masses of two metal balls.
One ball is made of
aluminum and the other ball is made of lead. The student adds 50 mL
of water to each graduated cylinder and then drops one metal ball into
each graduated cylinder. The teacher asks the student to use the
information she collected to compare the density of the two metal balls.
The mass of the lead ball is 113 grams and the mass of the aluminum
ball is 27 grams.
2. What can be concluded about the density
of these metal balls based on this
investigation?
A. The density of both metal balls is the
same.
B. The density of both metal balls is less
than the density of the water.
C. The density of the lead ball is less than
the density of the aluminum ball.
D. The density of the lead ball is greater
than the density of the aluminum ball.
2) What can be concluded about the density of these
metal balls based on this investigation?
A. The density of both metal balls is the same.
If a student chooses A, he or she may not
understand that while the volumes are equal, the
two balls have different masses, so they do not have
the same density.
B. The density of both metal balls is less than the
density of the water.
If a student chooses B, he or she may not
understand that the reason the balls sank is that their
densities are greater than the density of water.
C. The density of the lead ball is less than the density
of the aluminum ball.
If a student chooses C, he or she may not
understand that the lead ball has a greater density
because its mass is greater than the mass of the
aluminum ball of equal volume.
D. The density of the lead ball is greater than the
density of the aluminum ball.
This is the correct answer.
The lead has more mass than, but the same volume
as, the aluminum ball, so the density (mass/volume)
of the lead ball has to be greater than the density
(mass/volume) of the aluminum ball.
Most electric power is generated by
burning fossil fuels. A family living in
central Ohio uses electric appliances
for cooking and air conditioning. They
use fuel oil for heating.
3) What change could this family
make to conserve fossil fuels?
A. convert to natural gas as a fuel for
cooking
B. switch to the use of less
expensive coal for heat
C. lower the temperature setting on
the air conditioner
D. install solar roof panels to
generate additional electricity
3) What change could this family make to conserve
fossil fuels?
A. convert to natural gas as a fuel for cooking
If a student chooses A, he or she may not understand
that natural gas is a fossil fuel, so switching from
electricity to natural gas would not save or conserve
fossil fuels.
B. switch to the use of less expensive coal for heat
If a student chooses B, he or she may not understand
that switching from fuel oil to coal would not
conserve fossil fuels, since they are both fossil fuels.
C. lower the temperature setting on the air conditioner
If a student chooses C, he or she may not understand
that turning the temperature down would actually use
more electric energy (since lowering the temperature
makes the air colder and uses more energy). The
temperature would have to be set higher in order to
save or conserve electricity.
D. install solar roof panels to generate additional
electricity
This is the correct answer.
The use of solar panels to make electricity, which is
used to operate or use electric appliances in the home,
would save or conserve fossil fuels. Energy produced
this way takes the place of energy that would be made
by fossil fuels in electric power plants.
This table lists
the densities of
several
materials.
4) Which material will float
in water?
A. limestone
B. magnesium
C. sulfur
D. wax
4) Which material will float in water?
A. limestone
If a student chooses A, he or she may not
understand that if a material floats in water, its
density must be less than the density of water. The
density of limestone is greater than water so it
would not float in water.
B. magnesium
If a student chooses B, he or she may not
understand that if a material floats in water, its
density must be less than the density of water.
Magnesium has greater density than water so it
would not float in water.
C. sulfur
If a student chooses C, he or she may not
understand that a material must have a density of
less than one, which is the density of water, in order
to float in water.
D. wax
This is the correct answer.
Wax has a density that is less than the density of
water. For a material to float in water, it has to have
a density that is less than water. All other materials
in the table will sink in water because their densities
are greater than the density of water.
5) Why is coal considered to be
a nonrenewable energy
source?
A. Sunlight is the original
source of energy for coal.
B. The burning of coal could
cause environmental
pollution.
C. Once coal is mined, it can
take millions of years to be
replaced.
D. Coal is abundant, but it is
very expensive to mine from
underground.
5) Why is coal considered to be a nonrenewable energy source?
A. Sunlight is the original source of energy for coal.
If a student chooses A, he or she may have thought that the
question asked about the original source of energy that
makes coal, which is sunlight. But sunlight itself is a
renewable energy source.
B. The burning of coal could cause environmental pollution.
If a student chooses B, he or she may have thought that
environmental pollution is what makes coal a nonrenewable
resource. The burning of coal as a fuel adds to air pollution
and is dangerous for the environment, but this does not
explain why coal is a nonrenewable energy source. Coal is
nonrenewable because it takes millions of years to be
created.
C. Once coal is mined, it can take millions of years to be
replaced.
This is the correct answer.
Coal is a nonrenewable energy source because it takes a long
time to replace/renew the energy source compared to how
fast it is used. This means that it is used up faster than it is
replaced.
D. Coal is abundant, but it is very expensive to mine from
underground.
If a student chooses D, he or she may have thought that the
cost of mining a resource is why it is nonrenewable. The fact
that taking coal from underground is hard/expensive does not
have a lot to do with the time it would take to replace/renew
the resource. Coal is nonrenewable because it takes millions
of years to form.
Ms. William’s science class uses a toy car race to study and collect data
about forces and motion. The racetrack shown has a 6-meter ramp and a
5-meter section to the finish line. Two cars compete at a time.
6) On what section of the racetrack will
the forces on the cars be balanced?
A.
B.
C.
D.
the starting block
the ramp only
the level section after the ramp
the entire track
6) On what section of the racetrack will the forces on
the cars be balanced?
A. the starting block
This is the correct answer.
On the starting block, the cars are at a constant
speed of zero, so there is zero net force, which
means the forces are balanced.
B. the ramp only
If a student chooses B, he or she may have thought
that the effect of gravitational force on the cars
will be balanced. But the speed of the cars is
increasing (the cars are accelerating), so there is an
unbalanced force pulling the cars down the ramp.
C. the level section after the ramp
If a student chooses C, he or she may have thought
that the forces on the cars are balanced. But when
the cars decelerate (slow down), there is an
unbalanced force slowing down the cars.
D. the entire track
If a student chooses D, he or she may have thought
that the forces acting on the cars are always
balanced, without thinking about where the cars
are on the track. However, the speed of the car is
changing everywhere on the track except at the
starting block.
Assume this car is on the ramp as in
question #6. In the diagrams below, g is the
force of gravity, r is the force of the ramp
acting on the car and f is the force of
friction.
7) Which diagram shows the directions of
the forces acting on a car as it travels
down the ramp?
A.
B.
C.
D.
7) On what section of the racetrack will the forces on
the cars be balanced?
A. the starting block
This is the correct answer.
On the starting block, the cars are at a constant
speed of zero, so there is zero net force, which
means the forces are balanced.
B. the ramp only
If a student chooses B, he or she may have thought
that the effect of gravitational force on the cars will
be balanced. But the speed of the cars is increasing
(the cars are accelerating), so there is an unbalanced
force pulling the cars down the ramp.
C. the level section after the ramp
If a student chooses C, he or she may have thought
that the forces on the cars are balanced. But when
the cars decelerate (slow down), there is an
unbalanced force slowing down the cars.
D. the entire track
If a student chooses D, he or she may have thought
that the forces acting on the cars are always
balanced, without thinking about where the cars are
on the track. However, the speed of the car is
changing everywhere on the track except at the
starting block.
Electricity is produced in a
hydroelectric plant when
moving water turns a turbine.
8) Which describes this energy
transformation from the
turning turbine to electricity?
A. kinetic energy into electric
energy
B. nuclear energy into electric
energy
C. thermal energy into electric
energy
D. chemical energy into electric
energy
8) Which describes this energy transformation from
the turning turbine to electricity?
A. kinetic energy into electric energy
This is the correct answer.
The kinetic energy of moving water turns the
turbine. The turning turbine (kinetic energy of the
turbine) changes into electric energy.
B. nuclear energy into electric energy
If a student chooses B, he or she may have
thought that a hydroelectric plant uses nuclear
energy, but nuclear energy doesn’t have any part
in a hydroelectric plant.
C. thermal energy into electric energy
If a student chooses C, he or she may have
thought that thermal energy of the water is used to
make electricity in a hydroelectric plant, but in a
hydroelectric plant the kinetic energy of water is
changed into electric energy.
D. chemical energy into electric energy
If a student chooses D, he or she may have
thought that a hydroelectric plant uses chemical
energy from the water to make electricity, but
chemical energy is not used. The kinetic energy
of the water is changed into electric energy.