Answer: 4800 N/m
Explanation:
Given
mass of rock 
Height of cliff 
compression in the spring 
Here, potential energy is converted into kinetic energy which in turn converts to elastic potential energy of the spring

Answer:
50N
Explanation:
the net force is the addition of all forces in an object.
The frictional force is the opposite of the applied force, so:
Nf(net force)= 250(applied force)-200(frictional force)
so Nf=50N
(a) 159 nm
First of all, let's calculate the energy difference between the level E1 and E4:

Now we know that this energy difference is related to the wavelength of the absorbed photon by

where
is the Planck constant
is the speed of light
is the wavelength of the photon
Solving for
, we find

b) 293 nm
As done in part a), let's calculate the energy difference between the level E2 and E3:

this energy difference is related to the wavelength of the absorbed photon by

Solving for
again, we find

c) 226 nm
As done in part a) and b), let's calculate the energy difference between the level E1 and E3:

this energy difference is related to the wavelength of the emitted photon by

Solving for
again, we find

Answer:
when a force is applied by one object to a second object, an equal and opposite force is applied back on the first object
Explanation:
<span>From the
small number of impact craters on moon, planetary geologists suspect
that virtually all its original surface has been covered over by younger
volcanic activity</span>. Most
of the Moon's surface is densely covered with craters, but we find relatively few
craters within the lunar maria.<span> </span>