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56 Cards in this Set
- Front
- Back
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What are some types of energy?
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Electrical ,Gravitational (potential), Chemical/Biological, Heat, Light and EM waves ,Nuclear
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what is Energy?
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The capacity of a physical system to do work or any aspect of native that allows change to occur.
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Work
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the measure of energy transfer that occurs when an object is moved over a distance by an external force, some component of which is applied in the direction of displacement
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What is another way to say work
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NM=J
J= Jouls |
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power
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The rate at which work is done, expressed as the amount of work per unit time and commonly measured in units such as the watt and horsepower.
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Kinetic Energy
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Form of energy that an object has by reason of its motion. The kind of motion may be translation (motion along a path from one place to another), rotation about an axis, vibration, or any combination of motions.
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Potential Energy
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The energy of a particle or system of particles derived from position, or condition, rather than motion. A raised weight, coiled spring, or charged battery has potential energy.
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Two classes of work
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● Work done against another force
● Work done to change the speed of an object |
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Is any work being done on the brick wall?
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No
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Does the weight lifter do work on the barbell
– when lifting it over his head? – |
Yes
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Does the weight lifter do work on the barbell
when holding it over his head? |
No
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Velocity
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m/s
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Acceleration
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m/s2
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Force
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kg•m/s2 ≡ N (Newton)
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Work/Energy
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N•m ≡ J (Joule)
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Power is the amount of work done per unit time Does this mean that a car that is twice as powerful as another car has a top speed that is twice as fast?
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No. It means that a more powerful engine can accelerate
a car up to a given speed faster than a less powerful engine can. In this case, twice as quickly. |
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Kinetic Energy
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KE = ½ mass x speed2
Or KE = ½ mv2 |
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If you push for a half hour or a whole hour against a stationary wall,
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no work is done in either case.
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If you push an object twice as far while applying the same force, you do
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twice as much work.
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If you find that twice as much work is needed to perform a task but it takes twice as much time, the amount of power required is
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unchanged
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Do 100 J of work in 50 s and your power output is
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2 W.
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An object lifted 10 meters gains 200 J of potential energy. If the same object is lifted 20 meters, its potential energy gain is
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twice as much.
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When a car is braked to a stop, its kinetic energy is transformed to
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heat.
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A diver who weighs 500 N steps off a diving board that is 10 m above the water. The diver hits the water with kinetic energy of
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5000 J.
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A machine puts out 100 Watts of power for every 1000 Watts put into it. The efficiency of the machine is
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10%.
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No work is done by gravity on a bowling ball that rolls along a bowling alley because
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the force on the ball is at right angles to the ball's motion
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A woman carries a heavy box across a room at a constant speed. How much work does she do on the box while walking ?
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none
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It takes 40 J to push a large box 4 m across a floor. Assuming the push is in the same direction as the move, what is the magnitude of the force on the box?
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10 N
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The ball rolling down an incline has its maximum potential energy at
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the top.
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Two pool balls, each moving at 2 m/s, roll toward each other and collide. Suppose after bouncing apart, each moves at
4 m/s. This collision violates conservation of |
energy.
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If an object has kinetic energy, then it also must have
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momentum.
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A torque acting on an object tends to produce
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rotation.
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Stand a meter stick on its end and let go and it rotates to the floor. If you attach a heavy weight to its upper end and repeat, falling time will be
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more.
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Put a pipe over the end of a wrench when trying to turn a stubborn nut on a bolt, to effectively make the wrench handle twice as long, you'll multiply the torque by
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two
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Consider a string with several rocks tied along its length at equally spaced intervals. You whirl the string overhead so that the rocks follow circular paths. Compared to a rock in the middle of the string, a rock at the outer end moves
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twice as fast.
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A huge rotating cloud of particles in space gravitate together to form an increasingly dense ball. As it shrinks in size the
cloud |
rotates faster.
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Horses that move with the fastest linear speed on a merry-go-round are located
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near the outside.
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If you replace the wheels and tires of your car with new ones having greater diameters, all of your speedometer readings thereafter will
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decrease
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Suppose the circumference of a bicycle wheel is 2 meters. If it rotates at 1 revolution per second when you are riding the
bicycle, then your speed will be |
2 m/s.
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On a balanced see saw, a boy three times as heavy as his partner sits
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1/3 the distance from the fulcrum
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If the Earth had two identical moons in one circular orbit, and the moons were on opposite sides of the orbit, the center of gravity of the Earth-moons system would be
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at the center of the Earth.
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If the mass of the Earth somehow increased with no change in radius, your weight would
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increase also.
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Inside a freely-falling elevator, there would be no
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apparent weight for you.
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An asteroid exerts a 360-N gravitational force on a nearby spacecraft. If the spacecraft moves to a point 3 times as far
from the center of the asteroid, the force will be |
40 N.
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The reason the moon does not crash into the Earth is that the
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moon has a sufficient tangential speed and inertia.
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Which pulls on the oceans of the Earth with the greater force?
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the sun
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Which is most responsible for the ocean tides
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The moon
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During an eclipse of the sun the high ocean tides on Earth are
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extra high
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Earth satellites are typically more than 100 km high so as to be above the Earth's
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atmosphere
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A bullet fired horizontally over level ground hits the ground in 0.5 second. If it had been fired with twice the speed in the same direction, it would have hit the ground in
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0.5 s.
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Two projectiles are fired from ground level at equal speeds but different angles. One is fired at an angle of 30 degrees
and the other at 60 degrees. The projectile to hit the ground first will be the one fired at (neglect air resistance) |
30 degrees.
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What prevents satellites such as the space shuttle from falling?
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Nothing; they are continually falling as they orbit the Earth.
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If a moon orbits one of our most distant planets in an elliptical path. The distance that the moon covers each day is
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greatest when the moon is closest to the planet.
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A woman on the surface of the Earth has a mass of 50 kilograms and a weight of 490 newtons. If the woman were floating freely inside a space habitat far away from Earth, she would have
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less weight and the same mass.
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Minimal orbital speed about the Earth is about 8 km/s. Minimal orbital speed about the moon would be
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ess than 8 km/s.
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A satellite near the Earth makes a full circle in about an hour and a half. How long would a satellite located as far away
as the moon take to orbit the Earth? |
about 28 days
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