Not totally sure but i would say a normal? its not refraction or incidence if its perpendicular and i dont think its a mirror if its an imaginary line so yeah normal (normals are always perpendicular to their surface too i think so)
Answer: Relative motion
Explanation: If two objects are moving either towards or away from each other with both having their velocities in a reference frame and someone is outside this reference frame seeing the motion of the two objects.
The observer ( in his own frame of reference) will measure a different velocity as opposed to the velocities of the two object in their own reference frame. p
Both the velocity measured by the observer in his own reference frame and the velocity of both object in their reference is correct.
Velocities of this nature that have varying values based on motion referenced to another body is known as relative velocity.
Motion of this nature is known as relative motion.
<em>Note that the word reference frame is simply any where the motion is occurring and the specified laws of motion is valid</em>
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For this example of ours, the reference frame of the companion is the train and the telephone poles has their reference frame as the earth.
The companion will measure the velocity of the telephone poles relative to him and the velocity of the telephone pole relative to an observer outside the train will be of a different value.
The volume of the object must be no larger than
.
Explanation:
In order for an object to be able to float in water, its density must be equal or smaller than the water density.
The density of water is:

This means that the density of the object must be no larger than this value.
We also know that the density of an object is given by

where
m is the mass of the object
V is its volume
For the object in this problem, the mass is

Therefore, we can re-arrange the equation to find its volume:

So, the volume of the object must be no larger than
.
Learn more about density:
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The net force on the hanging object is zero. If it were not zero, then the object would be accelerating in some direction.
Kinetic energy than parked