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Work, Energy, Power
http://pingo.upb.de/511500
ConcepTest 1: Kinetic energy
Car #1 has twice the mass of car #2, but they both have
the same kinetic energy. How do their speeds compare?
1. 2 v1 = v2
2. √2 v1 = v2
3. 4 v1 = v2
4. v1 = v2
5. v1 = √2 v2
ConcepTest 1: Kinetic energy
Car #1 has twice the mass of car #2, but they both have
the same kinetic energy. How do their speeds compare?
2. √2 v1 = v2
Kinetic energy is proportional to the mass and
proportional to the square of the velocity. Since the mass
of car #1 is twice the mass of car #2, the square of the
velocity of car #2 must be twice the square of the
velocity of car #1. Hence, the velocity of car #2 must be
√2 times the velocity of car #1.
ConcepTest 2: Potential energy
You push a box halfway up a ramp, so that it has
potential energy equal to Z. If you push the box all the
way up the ramp, the potential energy will be
1. equal to Z.
2. greater than Z, but less than 2 Z.
3. equal to 2 Z.
4. one-half Z.
5. impossible to determine
ConcepTest 2: Potential energy
You push a box halfway up a ramp, so that it has
potential energy equal to Z. If you push the box all the
way up the ramp, the potential energy will be
3. equal to 2 Z.
The gravitational potential energy is proportional to the
mass and to the height. Since the mass is fixed and the
height is doubled, the potential energy is also doubled.
ConcepTest 3: Conservation of energy
Two marbles, one twice as heavy as the other, are
dropped to the ground from the roof of a building. For
these small marbles, air resistance is negligible. Just
before hitting the ground, the heavier marble has
1. as much kinetic energy as the lighter one.
2. twice as much kinetic energy as the lighter one.
3. half as much kinetic energy as the lighter one.
4. four times as much kinetic energy as the lighter one.
5. impossible to determine
ConcepTest 3: Conservation of energy
Two marbles, one twice as heavy as the other, are
dropped to the ground from the roof of a building. For
these small marbles, air resistance is negligible. Just
before hitting the ground, the heavier marble has
2. twice as much kinetic energy as the lighter one.
Since they start out at the same height, the heavier
marble starts out with twice the gravitational potential
energy as the lighter one. Since potential energy is
proportional to mass, the heavier marble will lose twice
the amount of potential energy as the lighter one. Thus,
it ends up with twice the kinetic energy.