Transcript Work and Energy

Work and Energy:
Jeopardy Review Game
Kinetic
Energy
Potential
Energy
Machines
Work and
Power
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Bungee
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Calculate the kinetic energy of a
3 kg toy cart that moves at
4m/s.
24 J
A hammer falls off a rooftop and
strikes the ground with a certain KE.
If it fell from a roof that was four
times higher, how would its KE of
impact compare? Its speed of
impact?
KE would be 4X greater
Speed would be 2X greater
Answer this question in terms of
KE. Why does a small,
lightweight car generally have
better fuel economy than a big,
heavy car?
Smaller mass means less kinetic
energy for a given velocity.
A rollercoaster starts with a speed of
5.0 m/s at a point 45 m above the
bottom of the dip. Neglect friction,
what will be the speed of the
rollercoaster at the top of the next
slope, which is 30 m above the
bottom of the dip?
18 m/s
1/2mv2 + mgh = 1/2mv2 + mgh
masses cancel out – then you can solve
for the velocity at the top of the second
hill.
What is the minimum speed of the
ball at the bottom of its swing
(point B) in order for it to reach
point A, which is 1.0 m above the
bottom of the pendulum?
4.5 m/s
What will be the kinetic energy of an
arrow having a potential energy of
50J after it is shot from a bow?
50 J
What is the potential energy of a
spring that has a spring
constant of 250 N/m when it is
compressed 3.0 cm?
0.11 J
A 3.0 kg stone is dropped from
a height of 10.0 m, and strikes
the ground with a velocity of
7.00 m/s. What average force
of air friction acts on it as it
falls?
22.7 N
If a spring is compressed 0.25 m
and when it is released it causes a
5.0 kg block to move 0.45 m/s on a
frictionless surface, what is the k
value of this spring? What force was
exerted on the block?
16 N/m
4.1 N
In what two ways can a machine
alter an input force?
By changing the magnitude or
the direction.
What is the ideal mechanical
advantage of this ramp?
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What is the ideal
mechanical
advantage of this
pulley system? If it
requires an effort
force of 1500 N to
lift the 500 kg Load
what is the %
efficiency of the
pulley?
IMA = 4
83% efficiency
What is the IMA of each of the
level systems shown?
A=1
B=2
C = 0.5
Work is required to lift a barbell.
How many times more work is
required to lift the barbell three
times as high?
Three times the work.
How much power is required to do
100 J of work on an object in a time
of 0.5 s? How much power is
required if the same work is done in
1 second?
200 W
100 W
True or False:
A machine decreases the amount of
work done on an object.
False! Less force over a greater
distance.
Chris’s car can go from 0 to 100
km/h in 10 s. If the engine
delivered twice the power to the
wheels, how many seconds would it
take?
5 seconds
If a car traveling at 60 km/h will
skid 20 m when its brakes lock,
how far will it skid if it is
traveling at 120 km/h when its
brakes lock?
80 m
Describe how energy is transferred
during a bungee jump.
Gravitational PE to Kinetic Energy to
Spring Potential Energy then back to
KE and gravitational PE