Hot Seat

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Hot Seat

• Review Game

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c) kg m2/s2

• 1. The unit for work is Joules. What is an
  equivalent unit for work using meters, kilograms,
  and seconds?
• kg m/s2
• kg m2/s
• kg m2/s2
• kg2m/s2

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Stay the same

• 2. If Zippy pushes a stationary brick wall ten
  times harder than he did yesterday, what happens
  to the work done? (Increase, Decrease or Stay the
  same.)

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They are the same.

• 3. An 8.0 kg mass is moving with a speed of 2.0
  m/s. A 2.0 kg mass is moving with speed 4.0 m/s.
  Both objects encounter the same constant braking
  force and are brought to rest. How do their
  stopping distances compare?

?KE W ?KE W ½ 8(2)2 Fd ½
2(4)2 Fd 16/F d 16/F d
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1/9

• 4. An object hits a wall and bounces back with
  one-third its original speed. What is the ratio
  of the final kinetic energy to the initial
  kinetic energy?

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653 W

• 5. At what rate is a 50 kg boy using energy when
  he runs up a flight of stairs 8 m high in 6
  seconds?

P W/t P mgh/t P ?E/t P
50(9.8)(8)/6
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125 JW ?KE ½ mv2 ½ (10)(52)

• 6. A 10 kg mass is moving with a speed of 5.0
  m/s. How much work is required to stop the mass?

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Nine times farther.

• 7. You slam on the brakes of your car and skid a
  certain distance. If you had been traveling
  three times as fast, what distance would the car
  have skidded under the same conditions?

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a) Momentum

• 8. An object that has kinetic energy must have
  (mark all that apply)
• Momentum
• Acceleration
• A net force applied to it
• Potential Energy

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a) KE increases and PE decreases

• 9. An apple falls from a tree. Compare its
  kinetic energy to its potential energy as it
  falls.
• KE increases and PE decreases
• KE decreases and PE decreases
• KE increases and PE increases
• KE decreases and PE increases

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2 to 1

• 10. A car moves twice as fast as a truck and has
  half the mass of the truck. What is the ratio of
  the cars kinetic energy to the trucks kinetic
  energy?

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They rise to the same height.

• 11. A lightweight object and a very heavy object
  are sliding with equal speeds along a level
  frictionless surface. They both slide up the
  same frictionless hill. Which rises to a greater
  height?

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3.96 m/s

• 12. A 5.0 kg ball falls to the floor. When it is
  0.80 m above the floor, its potential energy
  exactly equals its kinetic energy. How fast is
  it moving?

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PEmax gt KEmax

• 13. A ball falls from the top of a building
  through the air (air friction is present) to the
  ground below. How does the KE just before
  striking the ground compare to the PE at the top
  of the building?

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5,371,200 J

• 14. How many joules of energy are used by a 2.0
  hp motor that runs for 1.0 hr? (1 hp 746 W)

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Four

• 15. If a skaters speed increases so he has twice
  the momentum, then his kinetic energy increases
  by what factor?

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hydrogen gas

• 16. Consider molecules of hydrogen gas and
  molecules of heavier oxygen gas that have the
  same kinetic energy. Which molecules have a
  greater speed?