Download Extra revision sheet grade 9 Quarter3 Forces In the space provided

Extra revision sheet grade 9
Quarter3
Forces
In the space provided, write the letter of the term or phrase that best completes
each statement or best answers each question.
______ 1. If you divide momentum by velocity, the result is the value of the
a. mass.
c. energy.
b. direction.
d. speed.
______ 2. A 10.0 kg dog chasing a rabbit north at 6.0 m/s has a momentum of
a. 0.6 kg m/s.
c. 60.0 m/s.
b. 60.0 kg m/s north.
d. 60.0 kg/s.
______ 3. When the velocity of an object changes, it is acted upon by a(n)
a. force.
c. momentum.
b. inertia.
d. deceleration.
______ 4. If the net force on an object is zero then the object has
a. reaction forces.
c. balanced forces.
b. action forces.
d. unbalanced forces.
______ 5. When objects are moved further apart from each other, the force of
gravity between them
a. increases.
c. decreases.
b. stays the same.
d. decreases at first then increases.
______ 6. The SI unit of force, named for the scientist who described the relationship
between motion and force, is called the
a. newton.
c. curie.
b. einstein.
d. pasteur.
______ 7. When air resistance balances the weight of an object that is falling, the
velocity
a. slowly decreases.
c. rapidly increases.
b. remains constant.
d. None of the above
______ 8. The weight of an object can be calculated by multiplying mass by
a. distance.
c. velocity.
b. speed.
d. free-fall acceleration.
______ 9. Which object does not have momentum?
a. a fish swimming in a pond
c. a rock by the side of the road
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b. a feather falling to the ground
d. a boulder rolling down a hill
______10. What is the reaction force when you place a cup on a table?
a. The force of the cup on the table.
b. The force of the table on the cup.
c. The force of gravity on the table.
d. The force of gravity on the cup.
Read each statement and write in the blank the word or words that best
completes the statement.
11. The free fall acceleration of an object under Earth’s gravity is directed
_____________________________________________________________________
.
12. Terminal velocity is defined as
_________________________________________
_____________________________________________________________________
.
13. When you kick a stone, your foot exerts a force on the stone and the stone
exerts a force _____________________ in size and _____________________ in
direction on your foot.
14. Orbital motion is a combination of _____________________ motion and free
fall.
15. An important safety feature in your car that is based on the concept of inertia
is the _____________________.
16. The gravitational force on an object _____________________ as the object’s
mass increases.
17. The path of a pitched ball is an example of____________________ motion.
18. An object changes its motion only if a force acts on it to change its speed or
direction. This is a statement of Newton’s _____________________.
19. Action and reaction forces always occur at _____________________ time.
20. Rearrange the equation for Newton’s second law of motion to define acceleration
in terms of force and mass. _____________________.
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Forces
MULTIPLE CHOICE
1. Which of the following is not a factor in calculating momentum?
a. mass
c. acceleration
b. direction
d. speed
2. If you divide momentum by velocity, the result is the value of the object’s
a. mass.
c. energy.
b. direction.
d. speed.
3. Whenever an object is standing still, the value(s) that is/are always zero is/are
a. speed.
c. momentum.
b. velocity.
d. All of the above
4. A 10.0 kg dog chasing a rabbit north at 6.0 m/s has a momentum of
a. 0.6 kg · m/s.
c. 60.0 m/s.
b. 60.0 kg · m/s north.
d. 60.0 kg/s.
5. If you are given the mass of an object in pounds, the time in seconds, and the
distance in feet, what
must you do before you can calculate the momentum in SI units?
a. convert the mass to kilograms
c. Both (a) and (b)
b. convert the distance to meters
d. None of the above
6. Weight is best described as
a. an object’s resistance to acceleration.
b. what causes an object to fall.
c. the downward force exerted on objects due to gravity.
d. a force solely dependent on an object’s mass.
7. When objects are moved further apart from each other, the force of gravity
a. increases.
b. stays the same.
c. decreases.
d. decreases at first and then increases.
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8. Of the following, the greatest gravitational force would occur between
a. a marble and a baseball 5 meters apart.
b. a loaded freighter on the high seas and Earth.
c. the moon and an astronaut standing on the moon.
d. the moon and Earth.
9. The law that states that every object maintains constant velocity unless acted on by
an unbalanced force is
a. Newton’s first law of motion.
c. Newton’s third law of motion.
b. Newton’s second law of motion.
d. the law of conservation of
momentum.
10. The law that states that for every action force there is an equal and opposite
reaction force is
a. Newton’s first law of motion
.
c. Newton’s third law of motion.
b. Newton’s second law of motion.
d. the law of conservation of momentum.
11. The law that states that the unbalanced force acting on an object equals the
object’s mass times its acceleration is
a. Newton’s first law of motion.
c. Newton’s third law of motion.
b. Newton’s second law of motion.
d. the law of conservation of momentum.
12. The SI unit of force, named for the scientist who described the relationship
between motion and force, is called the
a. newton.
b. einstein.
c. curie.
d. pasteur.
14. Which of the following units is used to measure acceleration in free fall?
a. m/s
c. m/s2
b. m · s
d. m2/s2
15. Which of the following equations is correct?
a. w = mg
c. w = g/m
b. w = m/g
d. w = g + m
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16. Which of the following is true?
a. Weight and mass are proportional but not equal.
b. Weight is the gravitational force an object experiences due to its mass.
c. The weight of an object on Earth is greater than the weight of the same object on
thesurface of the moon, but the object’s mass stays the same.
d. All of the above
17. When air resistance balances the weight of an object that is falling, the velocity
a. slowly decreases.
b. remains constant.
c. rapidly increases.
d. None of the above
19. Which object does not have momentum?
a. a fish swimming in a pond
c. a rock by the side of the road
b. a feather falling to the ground
d. a boulder rolling down a hill
20. What is the reaction force when you place a cup on a table?
a. the force of the cup on the table
c. the force of gravity on the table
b. the force of the table on the cup
d. the force of gravity on the cup
21. Earth pulls on the moon and holds the moon in its orbit. The moon pulls on Earth
with an equal and opposite force. This is an example of
a. Newton’s first law.
c. Newton’s third law.
b. Newton’s second law.
d. None of the above
22. What is the unbalanced force that slows down a ball rolling across the floor?
a. the force of friction
c. the force of inertia
b. the force of gravity
d. the force of momentum
23. If two objects with different masses and traveling with different velocities collide,
what law allows you to predict the motion of the objects after the collision?
a. the law of conservation of momentum
c. Newton’s third law
b. the law of universal gravitation
d. Newton’s second law
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24. Express the following as an equation: One newton is the force that can give an
object with a mass of 1 kg an acceleration of 1 m/s2.
a. 1 N = 1 kg ÷ 1 m/s2
c. 1 N = 1 m/s2 ÷ 1 kg
b. 1 N ´ 1 kg = 1 m/s2
d. 1 N = 1 kg ´ 1 m/s2
25. Which statement about action-reaction forces is incorrect?
a. There are always two of them.
c. They always act on the same object.
b. They are always equal.
d. They always occur at the same time.
26. When gravitational forces and air resistance equalize on an object that is falling
toward Earth and the object stops accelerating, what is the velocity of an object
called?
a. resultant velocity
c. instantaneous velocity
b. terminal velocity
d. average velocity
27. In the absence of air resistance, how would the acceleration of a 1.5 kg book and
the acceleration of a 15 kg rock differ if the objects were dropped from the same
height?
a. The book would accelerate twice as fast as the rock.
b. The rock would accelerate twice as fast as the book.
c. The book would accelerate ten times as fast as the rock.
d. They would not differ; they would be the same.
28. What happens immediately after a skydiver opens her parachute?
a. Air resistance greatly increases.
c. The skydiver’s speed greatly
increases.
b. The skydiver is in free fall.
d. The force of gravity greatly
increases.
COMPLETION
1. Mass times velocity equals ____________________.
2. According to Newton’s second law of motion, force is the product of
____________________ and ____________________.
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3. The tendency of an object at rest to remain at rest, or if moving, to continue moving
at a constant velocity is ____________________.
4. An object with a small mass has ____________________ inertia than an object
with a large mass.
5. Organisms that live in water don’t need as strong a skeletal structure as organisms
____________________.
6. The motion of an object resulting from only the force of gravity is
____________________.
7. The free fall acceleration of an object under Earth’s gravity is directed toward
____________________.
8. According to the universal gravitation equation, the gravitational force between two
objects decreases as ____________________ increases.
9. A situation known as ____________________ occurs when astronauts and their
surroundings all accelerate at the same rate.
10. When a satellite orbits a planet, two motions combine to form the satellite’s orbit,
____________________ and ____________________.
11. When throwing a dart at a target, you should always aim ____________________
the bull’s eye.
12. When you stand, your weight pushes down on the ground and the ground pushes
back with a force equal to your weight ____________________.
13. The value for acceleration of objects in free fall near Earth is
____________________.
14. Newton’s ____________________ law tells us how much an object’s speed will
be increased or decreased by an unbalanced force.
15. Mass is a measure of the amount of ____________________ in an object.
16. If the distance between two objects is quadrupled, the gravitational force between
them____________________ its original value.
17. When two billiard balls collide, the total change in momentum of the balls is
____________________.
18. The total momentum of objects before a collision ____________________ the
total momentum of the objects after a collision.
20. An example of an action-reaction pair is the action force when you jump down
onto a trampoline, your weight pushes down on the surface and the reaction force
when the trampoline pushes back up on you with a force ____________________.
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21. When the same amount of force is applied to two different masses, the smaller
mass will be accelerated ____________________ than the larger mass.
23. The ____________________ of an object remains constant while its
____________________ varies according to the gravitational force it experiences.
SHORT ANSWER
1. Which has greater momentum, a small pick-up truck traveling at 55 km/h or a fullsized bus traveling at the same speed? and explain why?
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2. In space, which would accelerate at a faster rate, the space station or an astronaut?
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3. A small sports car traveling south collides with a heavy truck traveling north. Both
vehicles are going at the same speed. Which will be moved off course by the collision
and in which direction?
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4. State Newton’s first law.
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5. State Newton’s second law.
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5. What does Newton’s First Law tell us about the direction of the object’s motion
when not acted on by an unbalanced force?
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7. Rearrange the equation for Newton’s second law of motion to define acceleration in
terms of force and mass.
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8. On the moon, objects weigh about one-sixth what they do on Earth. What does that
tell you about g, the free-fall acceleration, on the moon as compared to g on Earth?
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9. Define terminal velocity.
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PROBLEM
1. A large truck loaded with scrap steel weighs 1400 kg and is traveling north on the
interstate heading for Chicago. It has been averaging 48 km/h for the journey and has
traveled over 1450 km so far. It has just stopped to refuel. What is its current
momentum?
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2. A 2.5 kg box is sliding along a level floor. It is slowing down at a rate of 0.45 m/s2.
What is the force of friction the floor is exerting on the box?
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3. Calculate the horizontal force that must be applied to a 1300 kg vehicle to give it an
acceleration of 2.6 m/s2 on a level road.
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Work and Energy
In the space provided, write the letter of the term or phrase that best completes
each statement or best answers each question.
______ 1. A boy pushes on a parked car with a force of 200 N. The car does not
move. How much work does the boy do on the car?
a. 200 N
c. zero
b. 200 J
d. none of the above
______ 2. What are the units of work?
a. J
b. N_m
c. kg_m2/s2
d. all of the above
______ 3. A weightlifter presses a 400 N weight 0.5 m over his head in 2 seconds.
What is the power of the weightlifter?
a. 100 N
c. 400 watts
b. 25 watts
d. 100 watts
______ 4. A machine is a device that
a. requires less work to do a given task.
b. decreases the amount of work done by a given force.
c. increases energy.
d. can multiply and change the direction of an input force.
______ 5. What is the gravitational potential energy of a 54 kg box that is 8.0 m
above the ground?
a. 5500 J
c. 3400 J
b. 4300 J
d. 550 J
______ 6. Which of the following is an example of mechanical energy?
a. nuclear energy
c. chemical energy
b. potential energy
d. light energy
______7. The primary source of the sun’s energy is
a. chemical energy.
c. nuclear fission.
b. nuclear fusion.
d. potential energy.
______8. Which of the following statements is not true?
a. The energy of a closed system is constant.
b. The energy of an open system can increase.
c. If the kinetic energy of an object decreases, the non mechanical energy will decrease.
d. Energy cannot be created or destroyed.
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______9. The efficiency of a ramp is 75%. If the amount of work input is 240 J,
what is the amount of useful work output?
a. 320 J
c. 240 J
b. 310 J
d. 180 J
______10. An object weighing 75 N is dropped from the top of a building and falls
a distance of 28 m to the ground. How much work does gravity do on
the object from the time it is dropped to the time it hits the ground?
a. zero
c. 2100 J
b. 75 J
d. 4625 J
Read each statement and write in the blank the word or words that best
completes the statement.
1. A quantity that measures the rate at which work is done is called
____________________.
2. Power is calculated by dividing work by ____________________.
3. Horsepower is the common unit of power in rating engines. However, the
official SI unit of power is the ____________________.
4. A __________________________ is defined as a machine made up of more
than one simple machine.
5. The formula for calculating kinetic energy can be written as
__________________________.
6. The stored energy resulting from the relative positions of objects in a system
is called ____________________.
7. The sum of the kinetic and potential energy of large-scale objects in a system
is called __________________________.
8. The source of the energy when dynamite explodes is ______ ____energy.
9. The source of the sun’s energy is ____________________.
10. A(n) ____________________ system exchanges energy with the outside.
11. The ratio of useful work output to work input is a measure of
____________________
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Work and Energy
MULTIPLE CHOICE
1. A boy pushes on a parked car with a force of 200 N. The car does not move. How
much work does the boy do on the car?
a. 200 N c. zero
b. 200 J d. can’t be determined
2. What are the units of work?
a. J
b. N·m
c. kg·m2/s2
d. All of the above
3. Which of the following processes requires the most work?
a. A 10 kg weight rests on a table.
b. A person holds a 1 kg weight still with outstretched arms.
c. A person lifts a 1 kg weight 1 m off the floor.
d. A 10 kg ball is rolled across the floor at a constant speed for a distance of 10 m.
4. A man pushes a crate along a factory floor by exerting a force of 55 N. If the crate
moves a distance of 4.0 m, how much work does the man perform?
a. 165 N
c. zero
b. 220 N
d. 145 J
5. What are the units of power?
a. watts
c. joules per second
b. horsepower
d. All of the above
6. A weightlifter presses a 400 N weight 0.5 m over his head in 2 seconds. What is the
power of the weightlifter?
a. 100 N
c. 400 watts
b. 25 watts
d. 100 watts
7. What is the mechanical advantage of a ramp that is 10 meters long and 2 meters
high?
a. 20
c. 8
b. 5
d. 15
8. A machine is a device that
a. requires less work to do a given task.
b. decreases the amount of work done by a given force.
c. increases energy.
d. can multiply and change the direction of an input force.
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9. Which of the following statements about work and energy is not true?
a. When work is done, energy is transferred or transformed.
b. Energy may be defined as the ability to do work.
c. Work and energy are always equal.
d. Work and energy have the same units.
10. What is the gravitational potential energy of a 55 kg box that is 8.0 m above the
ground?
a. 5500 J
c. 4300 J
b. 3400 J
d. 550 J
11. Gravitational potential energy depends on the
a. the mass of the object.
c. the acceleration due to gravity.
b. the height of the object.
d. All of the above
12. A medicine ball has a mass of 5 kg and is thrown with a speed of 2 m/s. What is
its kinetic energy?
a. 100 J
c. 2000 J
b. 10 J
d. 500 J
13. Which of the following is an example of mechanical energy?
a. nuclear energy
c. potential energy
b. chemical energy
d. light energy
14. The kind of energy associated with atomic bonds is
a. nuclear energy.
c. chemical energy.
b. light energy.
d. kinetic energy.
15. The primary source of the sun’s energy is
a. chemical energy.
b. nuclear fusion.
c. nuclear fission.
d. potential energy.
16. A pendulum is swinging back and forth and has a kinetic energy of 400 J at a
particular point in its path. Which of the following statements is not true?
a. Both the kinetic and potential energy are decreasing.
b. The minimum kinetic energy is zero.
c. When the kinetic energy is zero, the potential energy will be 400 J greater.
d. The potential energy increases when the kinetic energy decreases.
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17. Which of the following statements is not true?
a. The energy of a closed system is constant.
b. The energy of an open system can increase.
c. If the kinetic energy of an object decreases, the non mechanical energy will
decrease.
d. Energy cannot be created or destroyed.
18. An object weighing 75 N is dropped from the top of a building and falls a distance
of 28 m to the ground. How much work does gravity do on the object from the time it
is dropped to the time it hits the ground?
a. zero
c. 2100 J
b. 75 J
d. 4625 J
19. An object has a kinetic energy of 810 J after falling a certain distance. If the mass
of the object is 20kg, what is the speed of the object at this time?
a. cannot be determined
c. 8 m/s
b. 9 m/s
d. 7 m/s
20. The law of conservation of energy states that
a. the energy of a system can disappear.
b. it is impossible to make a perpetual motion machine.
c. energy cannot change form.
d. energy can neither be created nor destroyed.
COMPLETION
1. A quantity that measures the rate at which work is done is called
____________________.
2. A quantity that measures how much a machine multiplies force or distance is called
____________________.
3. Power is calculated by dividing work by ____________________.
4. Horsepower is the common unit of power in rating engines. However, the official
SI unit of power is the ____________________.
5. The ability to do work defines ____________________.
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6. The formula for calculating kinetic energy can be written as
____________________.
7. The stored energy resulting from the relative positions of objects in a system is
called
____________________.
8. The energy of a moving object due to its motion is called ____________________.
9. The sum of the kinetic and potential energy of large-scale objects in a system is
called
____________________.
10. Energy that lies at the level of atoms and does not affect motion on a large scale is
sometimes called____________________ energy.
11. The source of the energy when dynamite explodes is ____________________
energy.
12. The process that transforms light energy into chemical energy in plants is called
____________________.
13. The source of the sun’s energy is ____________________.
14. When a system exchanges energy with the environment outside the system, it is
called a(n)____________________.
15. The ratio of useful work output to work input is a measure of
____________________.
16. Energy is transferred as ____________________ when mechanical energy
decreases and temperature increases.
ESSAY
1. Three children exhaust themselves trying to push a large rock that doesn’t budge.
Have they done any work? Why?
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2. Do machines reduce the amount of work we have to do? If not, why are machines
so useful?
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3. Where does energy go when it seems to disappear?
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4. How does a pendulum show that there are non mechanical forms of energy?
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5. Why is light considered a form of energy?
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6. What is the law of conservation of energy?
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7. What is meant by the efficiency of a machine?
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solve all the practice problems in the text book
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