One thing that stringed, wind, and percussion instruments have in common in regard to the sounds they produce is that
a. the frequency is always a direct result of adjusting the length of the instrument.
b. the instruments are struck by tools to produce vibrations and sounds.
c. the sound originates from a vibration.
d. all of the instruments can be easily adjusted to produce a tone with a certain definite pitch.

jupiter is the largest planet in our solar system, having a mass and radius that are respectively, 318 and 11.2 times that of earth. suppose that an object falls from rest near the surface of each planet and that the acceleration due to gravity remains constant during the fall. each object falls the same distance before striking the ground. determine the ratio of the time of fall on jupiter to that on earth.

there are no contact forces mentioned on the list of choices that you've provided.