Force Work Power Motion study guide

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Force Work Power Motion study guide

• Solutions

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Formulas

• W Fd Joules J
• P W/t Watts W
• F ma Newtons N
• PE mgh Joules J
• KE .5mv2 Joules J
• a (vf-vi)/t meters/second2 m/s2
• ? mv kilogram meter/second kgm/s
• v d/t meters/second m/s

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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
• b.200 J
• c.zero
• d.cant be determined

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2. What are the units of work?

• a.J
• b.Nm
• c.kgm2/s2
• d.All of the above

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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.

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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
• b.220 N
• c.zero
• d.145 J

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5. What are the units of power?

• a.watts
• c.joules per second
• b.horsepower
• d.All of the above

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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
• b.25 watts
• c.400 watts
• d.100 watts

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8. 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.

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9. What is the gravitational potential energy of
a 55 kg box that is 8.0 m above the ground?

• a.5500 J
• b.3400 J
• c.4300 J
• d.550 J

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10. Gravitational potential energy depends on the

• a.the mass of the object.
• b.the height of the object.
• c.the acceleration due to gravity.
• d.All of the above

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11. 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
• b.10 J
• c.2000 J
• d.500 J

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12. Which of the following is an example of
mechanical energy?

• a.nuclear energy
• b.chemical energy
• c.potential energy
• d.light energy

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13. The kind of energy associated with atomic
bonds is

• a.nuclear energy.
• b.light energy.
• c.chemical energy.
• d.kinetic energy.

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14. The primary source of the suns energy is

• a.chemical energy.
• b.nuclear fusion.
• c.nuclear fission.
• d.potential energy.

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15. 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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16. 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 nonmechanical energy will decrease.
• d.Energy cannot be created or destroyed.

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17. 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
• b.75 J
• c.2100 J
• d.4625 J

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18. An object has a kinetic energy of 810 J after
falling a certain distance. If the mass of the
object is 20 kg, what is the speed of the object
at this time?

• a.cannot be determined
• b.9 m/s
• c.8 m/s
• d.7 m/s

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19. 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.

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20. The distance traveled by an object divided by
the time it takes to travel that distance is
called

• a.average velocity.
• b.average speed.
• c.average acceleration.
• d.activity.

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21. In order to determine speed, you must know

• a.time.
• b.distance
• c.Both (a) and (b)
• d.None of the above

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22. What is the speed of an object at rest?

• a.15 km/h
• b.0 km/h
• c.1 km/h
• d.This cannot be determined without further
  information.

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23. The difference between speed and velocity is
that velocity includes

• a.direction.
• b.distance.
• c.time.
• d.weight.

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24. An airplane is flying at 635 km per hour at
an altitude of 35 000 m. It is currently over
Kansas and is approximately 16 minutes ahead of
its scheduled arrival time. What is its velocity?

• a.635 km/h
• b.16 m/min
• c.35 000 m/s
• d.This cannot be determined without further
  information about its direction.

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25. Which of the following does not indicate
velocity?

• a.14 m/s SSE
• b.40 km/h toward the town square along the main
  street
• c.80 km/h going from New York toward New Jersey
• d.28 km from Los Angeles to Catalina Island

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26. Acceleration is defined as the change in
velocity divided by

• a.speed.
• b.final velocity.
• c.time.
• d.distance.

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27. The SI unit for acceleration is

• a.mph.
• b.ft/s2.
• c.m/s2.
• d.?v / t.

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28. On a velocity-time graph, a line with a
negative slope indicates that the object is

• a.speeding up.
• b.slowing down.
• c.not moving.
• d.traveling at a constant speed.

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29. When the velocity of an object changes, it is
acted upon by a(n)

• a.force.
• b.inertia.
• c.momentum.
• d.deceleration.

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30. Which straight-line acceleration indicates an
increase in speed?

• a.0 m/s2
• b.-15 m/s2
• c.4 m/s2
• d.All of the above

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31. Which of the following speeds is the most
accurate?

• a.100 meters per day
• b.100 meters per hour
• c.100 meters per minute
• d.100 meters per second

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32. 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.

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33. The law that states that every object
maintains constant velocity unless acted on by an
unbalanced force is

• a.Newtons first law of motion.
• b.Newtons second law of motion.
• c.Newtons third law of motion.
• d.the law of conservation of momentum.

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34. The law that states that for every action
force there is an equal and opposite reaction
force is

• a.Newtons first law of motion.
• b.Newtons second law of motion.
• c.Newtons third law of motion.
• d.the law of conservation of momentum.

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35. The law that states that the unbalanced force
acting on an object equals the objects mass
times its acceleration is

• a.Newtons first law of motion.
• b.Newtons second law of motion.
• c.Newtons third law of motion.
• d.the law of conservation of momentum.

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36. 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.

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37. One pound is equal to how many newtons?

• a.4.448 N
• b.2.2 N
• c.0.225 N
• d.12.5 N

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38 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.Newtons first law.
• b.Newtons second law.
• c.Newtons third law.
• d.None of the above

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39. Two gliders with the initial velocities and
masses shown below hit each other in a perfectly
elastic collision (elasticity 1.0). What will be
the velocity of glider 2 after the collision?

• A. 0.0 m/s
• B. 2.0 m/s
• C. 4.0 m/s
• D. 6.0 m/s

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39. Correct Answer D 6.0 m/s Explanation
Because the gliders have the same mass and the
collision is perfectly elastic, the gliders will
exchange velocities. This means that the velocity
of Glider 2 after the collision will be equal to
the velocity of Glider 1 before the collision.

• A. 0.0 m/s
• B. 2.0 m/s
• C. 4.0 m/s
• D. 6.0 m/s

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40. Glider 1 starts with a mass of 2.4 kg and a
velocity of 3.0 m/s. What is Glider 1's starting
momentum?

• A. 2.4 kgm/s
• B. 5.4 kgm/s
• C. 7.2 kgm/s
• D. 10.8 kgm/s

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40. Correct Answer C 7.2 kgm/s Explanation
Momentum is equal to mass times velocity, so 2.4
kg 3.0 m/s 7.2 kgm/s.

• A. 2.4 kgm/s
• B. 5.4 kgm/s
• C. 7.2 kgm/s
• D. 10.8 kgm/s

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41. Given the starting conditions shown below and
a perfectly elastic collision, what will be the
total momentum of both gliders after they
collide?

• A. -7.0 kgm/s
• B. -9.0 kgm/s
• C. -13.0 kgm/s
• D. -21.0 kgm/s

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41. Correct Answer B -9.0 kgm/s Explanation
By conservation of momentum, the total momentum
after the collision is equal to the total
momentum before the collision. The momentum of
glider 1 before the collision was2.0 kg 3.0
m/s 6.0 kgm/sThe momentum of glider 2 before
the collision was 3.0 kg -5.0 m/s -15.0
kgm/sTherefore the total momentum before and
after the collision was-15.0 kg m/s 6.0 kg
m/s -9.0 kgm/s

• A. -7.0 kgm/s
• B. -9.0 kgm/s
• C. -13.0 kgm/s
• D. -21.0 kgm/s

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42. Correct Answer A 6.4 m/s Explanation For
any elastic collision, the approach velocity is
equal to the separation velocity. The approach
velocity is equal to the difference of the two
velocities, v1 - v2. Therefore, the approach
velocity is 12.0 - (-16.0) 28.0 m/sThe
separation velocity is equal to the difference of
the two velocities after the collision, v2 - v1.
We know that the separation velocity is equal to
the approach velocity, and the velocity of the
first ball is given.v2 - (-21.6) 28.0v2 6.4
m/s

• A. 6.4 m/s
• B. 11.3 m/s
• C. 17.8 m/s
• D. 21.6 m/s

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42. Two balls collide head-on on a table. The
first ball has a mass of 0.50 kg and an initial
velocity of 12.0 m/s. The second ball has a mass
of 0.75 kg and an initial velocity of -16.0 m/s.
After the collision, the first ball travels at a
velocity of -21.6 m/s. What is the velocity of
the second ball after the collision? Assume a
perfectly elastic collision and no friction
between the balls and the table.

• A. 6.4 m/s
• B. 11.3 m/s
• C. 17.8 m/s
• D. 21.6 m/s

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42. Two balls collide head-on on a table. The
first ball has a mass of 0.50 kg and an initial
velocity of 12.0 m/s. The second ball has a mass
of 0.75 kg and an initial velocity of -16.0 m/s.
After the collision, the first ball travels at a
velocity of -21.6 m/s. What is the velocity of
the second ball after the collision? Assume a
perfectly elastic collision and no friction
between the balls and the table.

• A. 6.4 m/s
• B. 11.3 m/s
• C. 17.8 m/s
• D. 21.6 m/s

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43. Two gliders collide on an air track. Glider 1
has a mass of 7.0 kg, and glider 2 has a mass of
4.0 kg. Before the collision, glider 1 had a
velocity of 2.0 m/s, and glider 2 had a velocity
of -5.0 m/s. If the collision is perfectly
elastic, what is the total kinetic energy of both
gliders after the collision?

• -36.0 J
• B. 36.0 J
• C. 64.0 J D. 128.0 J

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43. Correct Answer C 64.0 J Explanation In
any collision, the total amount of energy in the
system is conserved. If the collision is
perfectly elastic, no heat or sound is produced
and the total kinetic energy is conserved.
Therefore, the total kinetic energy after the
collision is equal to the total kinetic energy
before the collision. Kinetic energy is equal to
mv2 / 2,KE1 7.0 2.02 / 2 14.0 JKE1 4.0
(-5.0)2 / 2 50.0 JTherefore, the total
kinetic energy before and after the collision is
64.0 J.

• -36.0 J
• B. 36.0 J
• C. 64.0 J
• D. 128.0 J

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44. Which of the following is not a factor in
calculating momentum?

• a.mass
• b.direction
• c.acceleration
• d.speed

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45. If you divide momentum by velocity, the
result is the value of the objects

• a.mass.
• b.direction.
• c.energy.
• d.speed.

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46. Whenever an object is standing still, the
value(s) that is/are always zero is/are

• a.speed. b.velocity.. c.momentum d.All of
  the above

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47. A 10.0 kg dog chasing a rabbit north at 6.0
m/s has a momentum of

• a.0.6 kg m/s.
• b.60.0 kg m/s north.
• c.60.0 m/s.
• d.60.0 kg/s.

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48. 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
• b.convert the distance to meters
• c.Both (a) and (b)
• d.none of the above

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49. Weight is best described as

• a.an objects 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 objects mass.

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50. Which of the following equations is correct?

• a.w mg
• b.w m/g
• c.w g/m
• d.w g m

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51. Which object does not have momentum?

• a.a fish swimming in a pond
• b.a feather falling to the ground
• c.a rock by the side of the road
• d.a boulder rolling down a hill

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52. 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
• b.the law of universal gravitation
• c.Newtons third law
• d.Newtons second law

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53. 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
• b.1 N x 1 kg 1 m/s2
• c.1 N 1 m/s2 1 kg
• d.1 N 1 kg x 1 m/s2