Answer:
the unit of work is derived unit because joule is defined the work done by the force aftab 1 newton causing the displacement of one metre something newton metre(n-m) is also used to measuring work.
The force of gravity between the astronauts is 
Explanation:
The magnitude of the gravitational force between two objects is given by:
where
:
is the gravitational constant
are the masses of the two objects
r is the separation between them
In this problem, we have two astronauts, whose masses are:

While the separation between the astronauts is
r = 2 m
Substituting into the equation, we can find the gravitational force between the two astronauts:

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Answer:
Light refracts when its speed changes as it enters a new medium.
Explanation:
Bending of light wave while it entering a medium with different speed is called refraction of light. Light passing from a faster medium to the slower medium bends the light rays toward the normal to boundary between two media. The amount of the bending of light depends on refractive index of the two media which is described by the Snell's Law. The angle of incidence is not equal to angle of refraction. Rainbow is caused but this refraction phenomena. Also Refraction is used in magnifying glasses, prism and lenses