<h2>
Answer: 0.17</h2>
Explanation:
The Stefan-Boltzmann law establishes that a black body (an ideal body that absorbs or emits all the radiation that incides on it) "emits thermal radiation with a total hemispheric emissive power proportional to the fourth power of its temperature":
(1)
Where:
is the energy radiated by a blackbody radiator per second, per unit area (in Watts). Knowing 
is the Stefan-Boltzmann's constant.
is the Surface area of the body
is the effective temperature of the body (its surface absolute temperature) in Kelvin.
However, there is no ideal black body (ideal radiator) although the radiation of stars like our Sun is quite close. So, in the case of this body, we will use the Stefan-Boltzmann law for real radiator bodies:
(2)
Where 
is the body's emissivity
(the value we want to find)
Isolating from (2):
(3)
Solving:
(4)
Finally:
(5) This is the body's emissivity
Answer:
20 5/6 sec
Explanation:
To find the solution we divide 5000 by 240
However, when you see a problem, always try to simplify
5000/240=500/24=250/12=125/6
Now the division is much easier
20 5/6 sec
Answer:
No image will be observed.
Explanation:
Images that are created by mirrors are virtual images. This virtual image can only be seen by an observer. In this case, an infinite number of images or no image will be created here as both will be reflecting their own images. Light will continuously bounce back and forth reflecting the same image.
Answer:
Explanation:
Component of force F₁ in right direction = F₁cos37
= 12 x cos37 = 9.58 N .
Component of force F₂ in vertically upward direction = F₁sin37
= 12 x sin37 = 7.22 N .
a ) Let normal force be R
R + F₁sin37 = mg
R + 7.22 = 1.5 x 9.8 = 14.7
R = 7.48 N .
b )
Net force in horizontal direction = F₂ - F₁cos37
= F₂ - 9.58
This is equal to zero as body is moving with zero acceleration
F₂ - 9.58 = 0
F₂ = 9.58 N
c ) If body is moving with acceleration of 2.5 m /s² along the direction of F₂
F₂ - 9.58 = 1.5 x 2.5 = 3.75
F₂ = 13.33 N .
Answer:
He is incorrect. Dissolving salt in water and evaporation of the water are both physical changes. The reappearance of salt is evidence that the change was reversible by a physical change, so it could not be a chemical change.
