A sharp knife can more easily cut objects than can a dull knife because
A. sharp knives have edges that can fit between the molecules of the object.
B. a greater force can be applied with a sharp knife.
C. dull knives cannot apply large forces.
D. a greater pressure can be applied with a sharp knife.
Answer: D
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The transit method allows us in principle to find planets around
A) only a small fraction of stars that have planets. B) all stars that have planets of any kind. C) only stars of about the same mass and size as our Sun. D) only stars located within about 100 light-years of Earth.
Prior to the time when Luis and Walter Alvarez proposed that an impact led to the extinction of the dinosaurs, it was generally assumed that the dinosaurs had died out over a period of at least thousands to millions of years. Consider each piece of evidence listed below and sort it into the correct bin based on whether it supports a sudden cause for the demise of the dinosaurs or whether it could also be consistent with a gradual cause leading to their demise over many thousands or more years.
Note: The “K-T sediment layer” refers to the geological layer dating to about 65 million years ago that separates sediments that contain dinosaur fossils from those that do not.
All of the following hypothetical planets orbit a star with the same mass as the Sun (one solar mass)
Which one has the shortest orbital period? (If two objects would have the same orbital period to within a difference of less than 1% consider them as having identical periods.) A) Planet A: one Earth mass and 1 AU from the star B) Planet B: two Earth masses and 1 AU from the star C) Planet C: two Earth masses and 2 AU from the star D) Planets A and B E) Planets B and C F) All of them have the same period.
Which of the following statements about electromagnetic waves in free space are true? (There could be more than one correct choice.)
A) The higher-frequency waves have shorter wavelengths than the lower-frequency waves. B) The higher-frequency travel faster than the lower-frequency waves. C) The wavelengths of the visible waves are some of the longest electromagnetic waves. D) The wavelengths of the visible waves are some of the shortest electromagnetic waves. E) The electric field vector is always at right angles to the magnetic field vector.