Answer:

Given:
Radius of curvature (R) of a spherical mirror = 20
To Find:
Focal length (f)
Explanation:
Formula:

Substituting value of R in the equation:



Answer:
Action and reaction are equal but act in opposite directions
This is because Gravity exists everywhere in the universe.
<h3>What is Gravity?</h3>
This is the force of attraction which acts on all matters in the universe. Astronauts appear weightless while in orbiting the Earth because the space shuttle and the astronauts are in free fall around it.
They fall at the same rate as the space shuttle which is why the astronauts appear weightless.
Read more about Gravity here brainly.com/question/88039
Answer:
Average recoil force experienced by machine will be 200 N
Explanation:
We have give mass of each bullet m = 50 gram = 0.05 kg
There are 4 bullets
So mass of 4 bullets = 4×0.05 = 0.2 kg
Initial speed of the bullet u = 0 m/sec
And final speed of the bullet v = 1000 m/sec
So change in momentum 
Time is given per second so t = 1 sec
We know that force is equal to rate of change of momentum
So force will be equal to 
So average recoil force experienced by machine will be 200 N
Ok, let me see if I can help
Sound is caused by vibrations. These can pass through a solid, liquid, and gas. But not through vacuum because there are no particles