That speed is (1m / 0.003sec) = 333 and 1/3 meters per sec .
The medium is not necessarily, but <u>could</u> be, air at sea-level pressure.
Answer:
0.68 s
Explanation:
We are given that
Initial velocity of box=![u=13m/s](https://tex.z-dn.net/?f=u%3D13m%2Fs)
Final velocity of box=v=11.5 m/s
Distance=d=8.5 m
We have to find the time taken by box to slow by this amount.
We know that
![v^2-u^2=2as](https://tex.z-dn.net/?f=v%5E2-u%5E2%3D2as)
Substitute the values
![(11.5)^2-(13)^2=2a(8.5)](https://tex.z-dn.net/?f=%2811.5%29%5E2-%2813%29%5E2%3D2a%288.5%29)
![132.25-169=17a](https://tex.z-dn.net/?f=132.25-169%3D17a)
![-36.75=17a](https://tex.z-dn.net/?f=-36.75%3D17a)
![a=\frac{-36.75}{17}=-2.2m/s^2](https://tex.z-dn.net/?f=a%3D%5Cfrac%7B-36.75%7D%7B17%7D%3D-2.2m%2Fs%5E2)
We know that
Acceleration=![a=\frac{v-u}{t}](https://tex.z-dn.net/?f=a%3D%5Cfrac%7Bv-u%7D%7Bt%7D)
Substitute the values
![-2.2=\frac{11.5-13}{t}](https://tex.z-dn.net/?f=-2.2%3D%5Cfrac%7B11.5-13%7D%7Bt%7D)
![-2.2=\frac{-1.5}{t}](https://tex.z-dn.net/?f=-2.2%3D%5Cfrac%7B-1.5%7D%7Bt%7D)
![t=\frac{1.5}{2.2}=0.68 s](https://tex.z-dn.net/?f=t%3D%5Cfrac%7B1.5%7D%7B2.2%7D%3D0.68%20s)
Hence, the time taken by box to slow by this amount=0.68 s
Answer:
123.18 nm
Explanation:
Given:
- Refractive index of the glass=1.5
- Index of magnesium fluoride=1.38
- Wavelength of the light =680 nm
Let t be the thickness of the film. The relation between the wavelength of light in film and thickness of the film in order to have no reflection is given by
![2t=\dfrac{\lambda_{film}}{2}\\t=\dfrac{\lambda_{film}}{4}](https://tex.z-dn.net/?f=2t%3D%5Cdfrac%7B%5Clambda_%7Bfilm%7D%7D%7B2%7D%5C%5Ct%3D%5Cdfrac%7B%5Clambda_%7Bfilm%7D%7D%7B4%7D)
Now According to question we have
![\lambda_{film}=\dfrac{\lambda_{film}}{n}](https://tex.z-dn.net/?f=%5Clambda_%7Bfilm%7D%3D%5Cdfrac%7B%5Clambda_%7Bfilm%7D%7D%7Bn%7D)
where n is the refractive index of the film.
![\lambda_{film}=\dfrac{680}{1.38}\\\lambda_{film}=492.75\ nm](https://tex.z-dn.net/?f=%5Clambda_%7Bfilm%7D%3D%5Cdfrac%7B680%7D%7B1.38%7D%5C%5C%5Clambda_%7Bfilm%7D%3D492.75%5C%20nm)
Now thickness t is given by
![t=\dfrac{492.75}{4}\\t=123.18\ \rm nm](https://tex.z-dn.net/?f=t%3D%5Cdfrac%7B492.75%7D%7B4%7D%5C%5Ct%3D123.18%5C%20%5Crm%20nm)
Hence the thickness of the film is calculated in order to have no reflection.
Forces of gravity depend on quantities of mass, whereas electrical forces depend on quantities of net charge.
If gravitational forces dominate over electrical forces, it can only be because the amounts of net charge involved are much much much much much smaller than the amounts of mass involved.
What I'm saying is ... this doesn't mean that there aren't huge amounts of electric charge present in stars, planets, comets, and other astronomical objects. But most of the charges are BALANCED ... there are equal amounts of positive and negative charge present in the same object, and there's very little of either kind <em>left over,</em> to be attracted or repelled by other objects.