Common terns hover in a stationary position over the ocean watching for a tasty fish. When they see one, they immediately stop their wings and simply free-fall into the ocean to catch the fish. Calculate how long a fish near the surface has to move away after the instant a tern sees it from a height of 3 m above the surface. Repeat Problem above, but now include air resistance. Assume a ball of 3 cm radius with an average density of 4400 kg/m 3 , a density of air of 1.3 kg/m 3 , and a value of C = 1.
In: Physics
Keynes wrote in The General Theory: “If we speak frankly, we have to admit that our basis of knowledge for estimating the yield ten years hence of a railway, a copper mine, a textile factory … amounts to little and sometimes to nothing”
Keynes was not talking about periods of turmoil and crisis when it might be expected that accurate information would be hard to come by; in his view, a state of “near ignorance” was the normal state of affairs.
Discuss Keynes’ concept of “uncertain” knowledge and what it may imply for our ability to measure risk and to invest, both in financial assets as well as in “real” businesses.
In: Economics
At the beach, some waves with wavelength of 100 m propagate towards the shore at a speed of 12.5 m/s. (c) Does the engine sound higher- or lower-pitched to someone standing on the shore, compared with the experience of people on the boat?
(a) Calculate the frequency that boat anchored near shore bobs up and down as the waves roll in.
(b) At what frequency the boat would bob up and down with if it were headed away from the shore at a speed of 4.8 m/s?
(c) At what frequency the boat would bob up and down with if it were headed toward the shore at a speed of 4.8 m/s?
In: Physics
1)The histone proteins of nucelosomes are often abnormally modified in cancer cells, leading to _____. a. an alteration in chromatin structure b. an alteration in levels of transcription c. double-stranded breaks in DNA d. All of the above e. Both a and b
2)
A DNA strand contains the sequence TCGGATGCACCT. A mutation happened that results in the sequence TCCGGATGCACCT. What type of mutation does this change represent?
|
a point mutation |
||
|
a missense mutation |
||
|
frameshift mutation |
||
|
a silent mutation |
3)
Chromosomal rearrangements might position a gene near heterochromatin. The gene's transcription
|
may be inverted. |
||
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may be amplified. |
||
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may cease. |
||
|
will turn on. |
In: Biology
In: Accounting
In: Physics
Experiment 2: Static Materials
In this experiment, you will investigate the phenomenon of static
electricity of various materials.
Materials
Electrostatics Kit Materials
*Paper (Any Kind)
*Flat Work Surface
Procedure
1. Tear the paper into small pieces (approximately the
size of a hole-punch) and scatter them in a small area on a table
or flat surface.
2. Choose one plastic strip (acetate [light blue and
transparent], vinyl [no color and transparent], or polyethylene
[white and translucent]) and one fabric (wool or cotton cloth) from
the electrostatics kit.
3. Quickly rub the fabric up and down the length of the
plastic strip for approximately 20 seconds.
4. Bring the plastic strip near the small, torn pieces
of paper.
5. Record observations about the amount picked up and
behavior of the paper in Table 2.
6. Repeat Steps 2 – 5 for five additional fabric and
plastic combinations.
Table 2: Static Electricity Properties of Various Materials
| Type of Plastic | Type of Fabric | Observations |
Post-Lab Questions
1. What happens when you bring the charged plastic strip near the paper pieces? Why does this happen?
2. Draw a free body diagram of the forces acting on the piece of paper.
3. Why does the electric force easily overcome the force of gravity and lift the paper off the surface without even touching the paper?
4. Which of the materials pick up positive charge
and which pick up negative charge? How did you determine
this?
In: Physics
5. Today Van de Graaff accelerators sometimes serve as “injectors” for other types of accelerators that then further increase the energy of the particles. Consider a Van de Graaff accelerator that is being used to accelerate protons. The high voltage terminal (metal sphere) of the Van de Graff is charged using a rubberized belt that is 30 cm wide and travels at a velocity of 20 m/s. Charge is sprayed onto the belt near the roller at the low voltage end and removed from the belt near the upper roller inside the high voltage terminal. The belt is given sufficient surface charge density at the lower roller to cause an electric field of 1.0 MV/m (i.e. approaching the breakdown field of air at atmospheric pressure which is ~ 3 MV/m) on each side of the belt. (a) What is the charging current delivered to the high voltage terminal in µA? Suppose we would like to accelerate the protons to an energy of 3 MeV. Take the radius of the spherical high voltage terminal to be the such that the electric field at the surface of the sphere just below the breakdown field of air (b) How long does it take to charge the high voltage terminal of the Van de Graaff from zero volts to 3 MV? The beam of 3 MeV protons is focused onto a lithium target. The beam is equivalent to a current of 5 µA. (c) At what rate do protons strike the target? (d) At what rate is energy (heat) produced in the target? (e) Would you consider the Van de Graaff a ‘source of emf ? Why or why not?
In: Physics
Select the experiments that use a randomized comparative design.
Environmental scientists are concerned with the effects of nitrogen on the drinking water supply. Hundreds of farmers have volunteered to participate in the study in exchange for free fertilizer. The scientists assign the low-nitrogen blend to 25 randomly chosen farms near rivers, creeks, and tributaries and assign the normal blend to 25 randomly chosen farms not near such bodies of water. The scientists then compare mean biomass production in grams per square meter during the growing season.
Participants in a study to determine the effects of a new cholesterol drug are divided into groups based on gender. All males receive the new drug, and all females receive a currently approved drug.
A gas company offers three plans to customers. The company randomly chooses 200 customers who have signed up for each of the three plans. It then compares their gas bills over six months to determine which plan saves customers the most money.
To test a new epidermal treatment on fish in polluted pond water, 60 fish with epidermal abrasions from the same pond are randomly placed into three groups. One group receives the new treatment, another group receives the existing treatment, and the third group receives no treatment.
Students have volunteered to participate in a study of the effects of caffeine on memory. A computer program assigns each student at random to drink either a caffeinated or a decaffeinated beverage. The students are then given a list of 20 different objects to study for one minute and asked to write down as many of the new objects as they can remember.
In: Statistics and Probability
1. Electric charge is
| A property of matter that is distinct from energy, momentum, mass, velocity, and acceleration. |
| A property of matter that is determined by the energy of an object. |
| A property of matter that related directly to the momentum of an object. |
2.
After rubbing a plastic ruler with a felt cloth, the ruler becomes negatively charged because:
| The cloth destroyed positive charges in the ruler. |
| The kinetic energy lost to friction was converted into positive charges. |
| The negative charges were transferred from the cloth to the ruler. |
| The positive charges were transferred from the cloth to the ruler. |
|
The potential energy lost to friction was converted into negative charges. 3. Electric charge is conserved, meaning _______.
|
4.
Metals are typically ______________,
they allow charge to move freely.
Materials like wood, rubber, and plastic are _______________,
they do not allow charges to move freely.
| conductors, insulators |
| insulators, conductors |
| conductors, semiconductors |
| semiconductors, conductors |
| semiconductors, insulators |
5.
When a negatively-charged object is brought close to a neutral conductor, but does not touch it, what happens?
| The free electrons in the conductor move closer to the negatively charged object, separating the charge in the conductor so it is more positive near the object. |
| The free electrons in the conductor move away from to the negatively charged object, separating the charge in the conductor so it is more positive near the object. |
| None of the above. |
In: Physics