Physics Final
A pendulum swings through 1 complete cycle every 2 s. Its frequency is
0.5 Hz.
physics meaning of work
=mechanical means of transferring energy. Work= force times distance (where force and distance are in the same direction. Work is a scalar quantity ( no direction ) The unit of work is a joule. - 1 joule =(1 newton)x(1 meter ) -J= N times m -1J= 0.7376 ft times pounds
What is a CT scan?
A series of x-ray images taken from different angles Source and detector rotate around object - projections from many angles • Many separate X-ray images produce CT database - x-rays from different angles mix shadows differently • Image is computed from the projections
Which will have a greater acceleration rolling down an incline: a hoop or a disk?
A solid disk has less rotational inertial and will accelerate more.
What is the difference between a vibrational node and a vibrational antinode?
An antinode is the location where constructive interference of the incoming and reflected waves creates the maximum amplitude of the wave. In contrast, a node is the location where destructive interference diminishes the wave amplitude to zero.
If a skater who is spinning pulls her arms in so as to reduce her rotational inertia by half, by how much will her angular momentum change? By how much will her rate of spin increase?
Angular momentum remains the same, while her rate of spin doubles.
two bricks are dropped to the ground from the same height. brick B weights twice as much as brick A. When brick B strikes the ground it has 1. half as much KE as brick A. 2. as much KE as brick A. 3. twice as much KE as brick A. 4. four times as much KE as brick A. 5. impossible to determine
Answer: 3. Remember that weight and mass are proportional to each other so brick B weighs twice as much as brick A and as well, brick B's mass is twice Brick A's weight. Gravitational potential energy is being converted into kinetic energy. The gravitational potential energy from brick A would be mass x acceleration due to gravity x the height. Brick B has twice the mass of Brick A so the gravitational potential energy would be 2mgh so brick B has twice the gravitational potential energy as Brick A THEREFORE the brick will have twice as much KINETIC ENERGY AS BRICK A.
Which requires more work: lifting a 50-kg sack a vertical distance of 2 m or lifting a 25-kg sack a vertical distance of 4 m?
Both take the same 1000 J.
CT vs MRI
CT is more widely used than MRI. X-rays (CT) are better for imaging bone while MRI is better for imaging organs, soft tissue an internal structures CT is fast ( few seconds), while MRI is slow (sparse MRI ~5-10 mins, abdomen or brain may take 30-40 mins). • MRI does not have ionizing-radiation.
Which is easier to get swinging: a baseball bat held at the narrow end or a bat held closer to the massive end (choked up)?
Easier to get swinging when held closer to the massive end.
How is evaporation related to sweating?
Evaporation of sweat is important in cooling our bodies when we overheat. Sweating is a cooling process. Water on our skin absorbs body heat as evaporation cools the body. Helps to maintain a stable body temperature.
What is the relationship between center of gravity and the support base for an object that is in stable equilibrium?
For stable equilibrium, the CG must be above a support base, and not extend beyond it.
What does it mean to say that evaporation is a cooling process?
For water molecules to go from a liquid to an energized gaseous state, they must first absorb heat energy. They do this by colliding with other water molecules. Evaporation is called a "cooling process" because it removes heat from the surrounding air.
How is Temperature different than heat?
Heat describes the transfer of thermal energy between molecules within a system and is measured in Joules. Heat measures how energy moves or flows. ... Temperaturedescribes the average kinetic energy of molecules within a material or system and is measured in Celsius (°C), Kelvin(K), Fahrenheit (°F), or Rankine (R). Heat, qstart text, q, end text, is thermal energy transferred from a hotter system to a cooler system that are in contact. Temperature is a measure of the average kinetic energy of the atoms or molecules in the system.
Heat
Heat is energy transferred because of a temperature difference, Heat is energy that flows between objects because of their difference in temperature Internal (thermal) energy on the move Technically, objects don't contain "heat"
How do clockwise and counterclockwise torques compare when a system is balanced?
How do clockwise and counter clockwise torques compare when a system is balanced?
What can be imaged with an MRI?
Hydrogen nuclei are protons Protons are magnetic Superconducting electromagnets create a base magnetic field that aligns all of the tiny hydrogen nuclei, or protons, in the body Radiofrequency magnetic pulses from the machine cause those tiny magnets to move out of alignment temporarily. As they relax back into alignment with the magnetic field, they induce a current in the magnet. Different tissues have different relaxation times. organs of the chest and abdomen—including the heart, liver, biliary tract, kidneys, spleen, bowel, pancreas, and adrenal glands. pelvic organs including the bladder and the reproductive organs such as the uterus and ovaries in females and the prostate gland in males.
A barbell is raised a certain distance by a weightlifter and therefore has gravitational potential energy relative to the floor. If it were raised twice as high, how much gravitational potential energy would it have relative to the floor?
If it were raised twice as high, then it would have twice as much potential energy relative to the floor because the gravitational potential energy is directly proportional to the height. PE=weight × height
Distinguish between linear momentum and angular momentum.
Linear momentum involves straight-line motion; angular momentum involves rotational motion.
Does the man do work on the brick wall as he puts all his might as he pushes into it.
NO because distance =0. No work done.
A weightlifter lifts a weight over her head for 3 seconds. Is work being done?
No, there is no motion. Work = force times DISTANCE.
gravitational potential energy
Potential energy that depends on the height of an object. Gravitational potential energy is energy an object possesses because of its position in a gravitational field. The most common use of gravitational potential energy is for an object near the surface of the Earth where the gravitational acceleration can be assumed to be constant at about 9.8 m/s2. Since the zero of gravitational potential energy can be chosen at any point (like the choice of the zero of a coordinate system), the potential energy at a height h above that point is equal to the work which would be required to lift the object to that height with no net change in kinetic energy. Since the force required to lift it is equal to its weight, it follows that the gravitational potential energy is equal to its weight times the height to which it is lifted.
What is temperature?
Related to the random motion of atoms and molecules in a substance. Measure of internal energy. Temperature is the measure of the average translational kinetic energy per molecule in substance, measured in degrees celsius, Fahrenheit, or Kelvin
How are x-rays similar to light?
Relative to visible light, the velocity of x-rays in a vacuum is the same. X-rays are a type of light. When they've been excited, atoms emit packages of energy called photons. These make up every kind of light. X-rays are particularly energetic photons that are emitted by electrons outside the nucleus. higher frequency than visible light2. lower frequency than visible light
As distance increases between most of the mass of an object and its center of rotation, does rotational inertia increase or decrease?
Rotational inertia increases with increasing distance
What is rotational inertia, and how is it similar to inertia as studied in earlier lessons?
Rotational inertia is the resistance to a change in rotational motion, which is similar to plane inertia which is a resistance to a change in velocity.
Consider three axis of rotation of a pencil: along the lead, at right angles to the lead at the middle, and at right angles to the lead at one end. Rate the rotational inertias about each axis from smallest to largest.
Smallest when rotation is about the lead; next when at a right angle about the middle, and most when about a right angle at the end.
What are the units of measurement for tangential speed? For rotational speed?
T speed is meters per second; rotational speed in RPM (revolutions per minute) It is the ratio of distance traveled per unit time. Units of tangential speed are meters/second.
On a rotating turntable, does tangential speed or rotational speed vary with distance from the center?
Tangential speed increases with distance. Rotational speed is constant.
Why is it important to hit a baseball at the bat's vibrational node?
The bat doesn't vibrate and more energy goes into the ball
Why is it important to hit a baseball at the bat's center of percussion (COP)?
The bat's backward and rotational motions balance resulting in zero net force at the pivot
Two cars are raised to the same elevation on service-station lifts. If one car is twice as massive as the other, how do their gains of potential energies compare
The car that is twice as massive as the other car has more potential energy because its' weight is twice as massive than the other car.
Inertia depends on mass; rotational inertia depends on mass and something else. What?
The distribution of mass about the axis of rotation
Elastic (spring) Energy potential
The energy stored in an object when the shape of the object is changed. The energy stored by the forces within a distorted elastic object. spring PE= 1/2 kd^2 k is the spring constant and d is the distance spring is compressed.
What is thermal (internal) energy?
The grand total of all energies inside a substance Kinetic and potential energies of atoms is responsible for temperature. An example is lifting a barbell. As the barbell is lifted chemical potential energy is converted into gravitational potential energy and thermal energy.
What is meant by "lever arm" of a torque?
The lever arm is the shortest distance between the applied force and rotational axis.
Work is being done to lift a barbell. How much work is done in lifting a barbell twice as heavy the same distance as the other?
This is in accord with work force distance. Twice the force for the same distance means twice the work done on the barbell.
Approximately where is the sweet spot located for most wooden bats?
To find one of the "sweet spots" on a baseball bat, hold the bat, hanging down, loosely between your thumb and index finger, just below the knob on the bat's handle. Have a friend tap the bat gently with a hammer, starting at the fat end and moving toward the handle. When the ball hits the bat at just the right spot (the "sweet spot"), the ball flies off the bat and you don't feel a thing in your hands.
What does torque tend to do to an object?
Torque tends to twist or change the state of rotation of the object. A torque tends to change the rotational motion of an object.
What two factors determine the location of a baseball bat's sweet spot?
When the ball hits the bat's center of percussion, -the bat's backward and rotational motions balance -the bat's handle doesn't jerk When the ball hits the bat's vibrational node, - the bat doesn't vibrate- more energy goes into the ball
What is the center of percussion of a baseball bat and why is it important?
When the ball hits the bat's center of percussion, The bats backward and rotational motions balance and the bat's handle doesn't jerk. The center of Percussion (COP) is determined by pivoting the bat about a point on the handle 6-inches from the knob and measuring the time (the period of oscillation) required for the bat to swing back and forth through one cycle. An impact at the COP will result in zero net force at the pivot point. Impacts closer to the handle will result in a translational force at the pivot. Impacts closer to the barrel end will result attempt make the bat rotate about its center-of-mass, causing a force in the opposite direction at the pivot point. For impacts at the COP these two opposite forces are balanced.
Who discovered x-rays, and in what year?
Wilhelm Roentgen, Professor of Physics in Wurzburg, Bavaria, discovered X-rays in 1895—accidentally—while testing whether cathode rays could pass through glass.
What is the physics definition of work? Give an example of a person doing work on an object to transfer or remove energy from it.
Work, W, is energy transferred to or from an object by means of a force acting on the object. Energy transferred to the object is positive work, and energy transferred from the object is negative work. This is not the common meaning of the word "work" To do work on an object, energy must be transferred Throwing a baseball does work Pushing an immovable wall does not do work
What is the major difference between x-ray imaging and MRI?
X-rays are better for imaging bone while MRI is better for imaging organs, soft tissue an internal structures
Does the girl pushing the cement brick up the ramp to the highest point, and the boy lifting a similar cement box up the highest point.
Yes! Because both do the SAME work in lifting the block PE=PE
A weightlifter lifts a barbell over her head. Is work being done?
Yes, the motion and the force are in the same direction
example of work:
a weightlifter raising a barbell from the floor does work on the barbell
gravitational potential energy equation
gravitational PE=mgh m being mass and h being height
A sprinter has kinetic energy. If he speeds up until he is going 4 times as fast, how much kinetic energy does he have in comparison?
kinetic energy of an object is directly proportional to the square of its speed. That means that for a twofold increase in speed, the kinetic energy will increase by a factor of four. ... And for a fourfold increase in speed, the kinetic energy will increase by a factor of sixteen.
What does MRI stand for?
magnetic resonance imaging.
A vibrational anti-node is a position of
maximum amplitude
A vibrational node is a position of
minimum amplitude. When the ball hits the bat's vibrational node, the bat doesn't vibrate and more energy goes into the ball. Vibrations are minimized, right at the point we call the sweet spot.
Electromagnetic waves consist of
oscillating electric and magnetic fields.
elastic energy example
rubber band. Elastic potential energy is stored in the bent hockey stick. It is stored, as well, when the ball is compressed.
X-rays have
shorter wavelengths than visible light 2. comparable wavelengths to visible light 3. longer wavelengths than visible light
kinetic energy and its equation
the form of energy contained in an object's translational and rotational motion. The faster an object moves, the greater its kinetic energy Kinetic energy is zero for a stationary object For an object with mass m, and velocity v well below the speed of light: K=(1/2)mv2 The unit of kinetic energy is a joule (J) m is mass and v is velocity
To say that body A has a higher temperature than body B is to say that body A has more
translational kinetic energy per molecule
