They become old and explode.
Answer:
18.1347 m/s
Explanation:
t = Time taken
u = Initial velocity
v = Final velocity
s = Displacement
a = Acceleration
g = Acceleration due to gravity = 9.81 m/s² = a
![v^2-u^2=2as\\\Rightarrow s=\dfrac{v^2-u^2}{2a}\\\Rightarrow s=\dfrac{0^2-6.95^2}{2\times -9.81}\\\Rightarrow s=2.4619\ m](https://tex.z-dn.net/?f=v%5E2-u%5E2%3D2as%5C%5C%5CRightarrow%20s%3D%5Cdfrac%7Bv%5E2-u%5E2%7D%7B2a%7D%5C%5C%5CRightarrow%20s%3D%5Cdfrac%7B0%5E2-6.95%5E2%7D%7B2%5Ctimes%20-9.81%7D%5C%5C%5CRightarrow%20s%3D2.4619%5C%20m)
Total height the ball falls is 2.4619+14.3 = 16.7619 m
![v^2-u^2=2as\\\Rightarrow v=\sqrt{2as+u^2}\\\Rightarrow v=\sqrt{2\times 9.81\times 16.7619+0^2}\\\Rightarrow v=18.1347\ m/s](https://tex.z-dn.net/?f=v%5E2-u%5E2%3D2as%5C%5C%5CRightarrow%20v%3D%5Csqrt%7B2as%2Bu%5E2%7D%5C%5C%5CRightarrow%20v%3D%5Csqrt%7B2%5Ctimes%209.81%5Ctimes%2016.7619%2B0%5E2%7D%5C%5C%5CRightarrow%20v%3D18.1347%5C%20m%2Fs)
The speed at which the stone reaches the ground is 18.1347 m/s
power received will always remain same and does not depends on the distance
it will be same as the power of source
![P = 3 mW](https://tex.z-dn.net/?f=P%20%3D%203%20mW)
now the energy released by one photon is given as
![E = \frac{hc}{\lambda}](https://tex.z-dn.net/?f=E%20%3D%20%5Cfrac%7Bhc%7D%7B%5Clambda%7D)
![E = \frac{6.6* 10^{-34}* 3 * 10^8}{760 * 10^{-9}}](https://tex.z-dn.net/?f=E%20%3D%20%5Cfrac%7B6.6%2A%2010%5E%7B-34%7D%2A%203%20%2A%2010%5E8%7D%7B760%20%2A%2010%5E%7B-9%7D%7D)
![E = 2.6 * 10^{-19} J](https://tex.z-dn.net/?f=E%20%3D%202.6%20%2A%2010%5E%7B-19%7D%20J)
now let say N photons per second released
![N * 2.6 * 10^{-19} = 3 * 10^{-3}](https://tex.z-dn.net/?f=N%20%2A%202.6%20%2A%2010%5E%7B-19%7D%20%3D%203%20%2A%2010%5E%7B-3%7D)
![N = 1.15* 10^{16} per\: second](https://tex.z-dn.net/?f=N%20%3D%201.15%2A%2010%5E%7B16%7D%20per%5C%3A%20second)