the unsaturated fatty acids were separated by the method of _________ package.
it is generally accepted that the _________ electrons can exist only in the state that they have specific energy levels.
forecasting of concrete ___________ depth is an important part of the structural durability assesent.
category 2 fuel _____________________
category 3 home maintenance _____________________
category 4 health product ___________________
category 5 personal care ______________________
category 6 others ______________________
time chemist(s) major achievement(s) friedrich wöhler ( )
time chemist(s) major achievement(s) 1856 ( )
time chemist(s) major achievement(s) 1858 developed the concept of chemical structure
time chemist(s) major achievement(s) felix hoffmann ( ) ( )
time chemist(s) major achievement(s) / developed synthetic methods ( )
organic chemistry is closely conncected with biochemistry.
in 19th century, people began to adopt the term biochemistry in their studies.
the creation of vitamin b12 was an siginificant event in the history of organic chemistry.
synthetic methods gained huge progress and made it possible to increase the production of indigo.
according to the author, petroleum was demonstrated to have a botanic origin.
which of the following formulas is true for all types of motion?
which of the following ideas is helpful in understanding projectile motion?
if the motional equation of a particle is expressed as , which of the following statement is true?
if we choose two different reference frames to yze the motion of an object, the description of motion can be different.
in 1-dimentional motion, if we know the accelaration of an object, then its velocity can be expressed as:
if a particle has a constant speed, its acceleration equals 0.
in a circular motion, the acceleration is always perpendicular to the velocity.
a person stands on a bathroom scale in an elevator. when the scale reads only 75% of the person’s regular weight, he claims that the elevator must be moving downward. is he right?
newton's laws can be used in any reference frame.
a all block of mass m is released on a triangular block of mass m. if at the same time a force is applied to m, m remains rest relative to m. (assuming all surfaces are frictionless)
newton's second law says: the acceleration of an object is directly proportional to the net force acting on it and is inversely proportional to its ________. (one word)
a 1500-kg car moving at 20m/s crosses the rounded top of a hill (treat as an arc of circle, radius 100m). what is the normal force n acted by the hill? (g=9.80m/s^2) n = _________ n
an object of mass 0.50 kg, hanging from a spring with a spring constant of 8.0 n/m, is set into a simple harmonic motion. what is the maximum speed of the object if its maximum displacement is 0.10 m?
which of the following statements is not necessarily true regarding mechanical waves?
a uniform circular motion on xoy plane can be treated as the superposition of a simple harmonic motion in x direction and another simple harmonic motion in y direction.
when a wave travels in medium, the particles in medium will oscillate with the same frequency, same amplitude and same phase.
consider an interference between two waves. at a certain position if the vibrations caused by two waves are in phase, they make a destructive interference.
what combination of optical phenomena causes the bright colored patterns sometimes seen on wet streets covered with a layer of oil?
suppose young’s double-slit experiment is performed in air using red light, and then it is done again in water. what happens to the interference pattern on the screen?
when there is a superposition between two rays of light from two different electric bulbs, we can not see interference fringes, because the coherent condition is not satisfied.
we can see atoms by visible light through an optical microscope.
if the incident angle is greater than brewster's angle, the reflection light will be plane-polarized.
white light (4000å~7000å) falls on a soap bubble (thickness t=3000å, n=1.3). light at which wavelength is maximally strengthened in the reflecting light? λ = __________ å