Chapter 5 Review
• Work may be measured using units of:
• Joules
• Your friend claims to have invented a
perpetual motion machine with an efficiency
of 110 percent. You tell him his invention is
impossible because it violates what law:
• Law of Conservation of Energy
• In science, work is defined as:
• Force time distance that an object moves in
the same direction
• Efficiency can be defined as the ratio of:
• Work output to Work input
• An electric food processor uses 10 joules of
electrical energy every second. Due to friction
and other causes, the energy available to spin
the blades to cut food is reduced to 5 joules
per second. The efficiency of the food
processor is:
• Wo/Wi
• 5 J/ 10J = 50%
• Calculate the work needed to lift a block
weighing 2 newtons a distance of 10 meters.
• W=Fd
• 2N(10m) = 20 N*m or 20 J
• How much power is necessary to do 50 joules
of work in 5 seconds?
• P = W/t
• 50 J / 5 s = 10 W
• A gallon of gasoline contains chemical energy. If you
pour a gallon of gasoline into your car, you could
drive for about 20 miles on the highway (about 20
minutes). You could choose instead to run a lawn
mower for an hour with one gallon of gasoline. If
the gasoline were to come in contact with a fire,
the entire gallon would burn in less than a minute.
Which reaction has the most power?
• A. Burning the gasoline in the car
• B. Burning the gasoline in a fire
• C. Burning the gasoline in the lawn mower
• D. They are equal because the gasoline has the
same chemical potential energy in each case.
• B
• The efficiency of most machines is less than
100 percent. Due to friction, energy seems to
be lost. While the energy is not truly lost, it
does work that is not useful or is converted to:
• Thermal energy or heat
• A marble rolls along the track below with no
friction. The sequence of positions on the track
listed in order from the lowest kinetic energy to
the highest kinetic energy is:
• 1, 5, 4, 2, 3, 6
• A moving car has kinetic energy. To bring the car
to rest, you must decrease its kinetic energy to
zero. The brakes do this work by applying a force
over a distance. What effect would doubling the
speed have on the braking distance?
• A. The braking distance would be 4 times smaller.
• B. The braking distance would be 2 times smaller.
• C. The braking distance would be 2 times greater.
• D. The braking distance would be 4 times greater.
• D
• Potential energy is energy due to the:
• Height or position of an object
• Exercise may transform the chemical energy in
the food you eat into what two types of
energy:
• KE and PE
• The amount of work performed over time
• Power
• The ability to do work
• energy
• Work done by a machine
• Work output
• Applied force that moves an object in the
direction of the applied force.
• Work
• This is traded for force to achieve a
mechanical advantage of more than one
• distance
• Work put into a machine
• Work input
• Ratio of the work output to the work input.
• Efficiency
•
•
•
•
•
•
Formulas you will need to complete the test.
P = W/t
W=fxd
Ek= (½)mv2
Ep = mgh
E = Wo/Wi x 100