Answer: 
Explanation:
The kinetic energy of an electron
is given by the following equation:
(1)
Where:

is the momentum of the electron
is the mass of the electron
From (1) we can find
:
(2)
(3)
Now, in order to find the wavelength of the electron
with this given kinetic energy (hence momentum), we will use the De Broglie wavelength equation:
(4)
Where:
is the Planck constant
So, we will use the value of
found in (3) for equation (4):
(5)
We are told the wavelength of the photon
is the same as the wavelength of the electron:
(6)
Therefore we will use this wavelength to find the energy of the photon
using the following equation:
(7)
Where
is the spped of light in vacuum
Finally:
Sound level at distance of 15 m is given as 20 dB
so intensity at this distance is given as



now if we move closer to some some distance the sound level is now 50 dB
now the intensity is given as



now we know that



so now the distance from friend must be 47 cm
Answer:
v = 15.65 m/s
Explanation:
We use conservation of mechanical energy between initial (i) and final (f) states:
Pi + KEi = Pf + KEf
At the top of the cave at the instant the bat starts to fall, there is only potential energy since the bat's velocity is zero.
Pi = m g h = 600 J
and the KEi = 0 J (no velocity)
Knowing the height of the cave's roof (12.8 m) , we can find the mass of the bat:
m = 600 J / (g 12.5) = 4.9 kg
Using conservation of mechanical energy, the final state is:
Pf + KEf = 600 J
with Pf = 0 (just touching the ground)
KEf= 1/2 4.9 (v^2)
and we solve for the velocity:
600 J = 0 + 1/2 4.9 (v^2)
v^2 = 600 * 2 / 4.9 = 244.9
v = 15.65 m/s
Answer & Explanation: Waste management are all activities and actions required to manage waste from its inception to its final disposal. There are several methods of managing waste with its strengths and weaknesses. The strengths include;
* It creates employment
* It keeps the environment clean
* The practice is highly lucrative
* It saves the earth and conserves energy
The weaknesses of the methods of waste management includes;
* The sites are often dangerous
* The process is mostly
* There is a need for global buy-in
* The resultant product had a short life