We can't see black holes because D) no light can get out
Explanation:
Black holes are the result of the gravitational collapse of a supermassive star.
The life of a supermassive star ends with a huge explosion, called supernova, that leaves behing a super-dense core called black hole.
Black holes are the most dense objects of the universe, having a huge mass in a super small size. For this reason, the gravitational force exerted by a black hole in its proximity is so strong that even light is not able to escape from the gravitational field. For this reason, light from a black hole is not able to reach us, and so we are not able to see these objects.
The "edge" of space beyond which light remains "trapped" inside the black hole is called event horizon, and no object can escape this region of space.
The radius of the event horizon of a black hole is called Schwarzschild radius and it is given by:

where
G is the gravitational constant
M is the mass of the black hole
c is the speed of light
Learn more about space:
brainly.com/question/2887352
brainly.com/question/10934170
#LearnwithBrainly
Answer:
the average speed in annual work out is 46.5
A) Calling F the intensity of the horizontal force and d the displacement of the block across the floor, the work done by the horizontal force is equal to

b) The work done by the frictional force against the motion of the block is equal to:


Part of these 105.1 Joules of work becomes increase of thermal energy of the block (

), and part of it becomes increase of thermal energy of the floor (

). We already know the increase in thermal energy of the block (38.2 J), so we can find the increase in thermal energy of the floor:

c) The net work done on the block is the work done by the horizontal force F minus the work done by the frictional force (the frictional force acts against the motion, so we must take it with a negative sign):

For the work-energy theorem, the work done on the block is equal to its increase of kinetic energy:

So, we have
Answer:
1 meter per second
Explanation:
Every second, he walks 1 meter because 15 ÷ 15 = 1