It would be "Double replacement".
Hope this helps!
A shock absorbent mattress is built such that the boxspring
of the bed absorbs pressure that is exerted to the bed. Hence, if you jump on
the mattress, you would not bounce up and down as much as a normal mattress
because the springs do not oscillate much. This is done to endure wear and
tear.
(a) 
The relationship beween centripetal acceleration and angular speed is
where
is the angular speed
r is the radius of the circular path
Here we gave
is the centripetal acceleration
r = 5.15 m is the radius
Solving for , we find:
(b) 21.3 m/s
The relationship between the linear speed and the angular speed is
where
v is the linear speed
is the angular speed
r is the radius of the circular path
In this problem we have
r = 5.15 m
Solving the equation for v, we find
No. A neutron star is the weird remains of a star that blew its outer layers off
in a nova event, and then had enough mass left so that gravity crushed its
electrons into its protons, and then what was left of it shrank down to a sphere
of unimaginably dense neutron soup. But it didn't have enough mass to go
any farther than that.
A black hole is the remains of a star that had enough mass to go even farther
than that. No force in the universe was able to stop it from contracting, so it
kept contracting until its mass occupied no volume ... zero. It became even
more weird, and is composed of a substance that we don't know anything about
and can't describe, and occupies zero volume.
Contrary to popular fairy tales, a black hole doesn't reach out and "suck things in".
It's just so small (zero) that things can get very close to it. You know that gravity
gets stronger as you get closer to an object, so if the object has no size at all, you
can get really really close to it, and THAT's where the gravity gets really strong.
You may weigh, let's say, 100 pounds on the Earth. But you're like 4,000 miles
from the center of the Earth. What if all of the earth's mass was crammed into
the size of a bean. Then you could get 1 inch from it, and at that distance from
the mass of the Earth, you would weigh 25,344,000,000 pounds.
But Earth's mass is not enough to make a black hole. That takes a minimum
of about 3 times the mass of the sun, which is right about 1 million times the
Earth's mass. THEN you can get a lightweight black hole.
Do you see how it works now ?
I know. It all seems too fantastic to be true.
It sure does.
