![19.2\:\text{m/s}](https://tex.z-dn.net/?f=19.2%5C%3A%5Ctext%7Bm%2Fs%7D)
Explanation:
At the top of the tree, the velocity of the pebble is purely horizontal so we can calculate it as
![v_{y} = v_{0y} = v_0\cos 40° = (25\:\text{m/s})(0.766)](https://tex.z-dn.net/?f=v_%7By%7D%20%3D%20v_%7B0y%7D%20%3D%20v_0%5Ccos%2040%C2%B0%20%3D%20%2825%5C%3A%5Ctext%7Bm%2Fs%7D%29%280.766%29)
![\:\:\:\:\:= 19.2\:\text{m/s}](https://tex.z-dn.net/?f=%5C%3A%5C%3A%5C%3A%5C%3A%5C%3A%3D%2019.2%5C%3A%5Ctext%7Bm%2Fs%7D)
Since the electron dropped from an energy level i to the ground state by emitting a single photon, this photon has an energy of 1.41 × 10⁻¹⁸ Joules.
<h3>How to calculate the photon energy?</h3>
In order to determine the photon energy of an electron, you should apply Planck-Einstein's equation.
Mathematically, the Planck-Einstein equation can be calculated by using this formula:
E = hf
<u>Where:</u>
In this scenario, this photon has an energy of 1.41 × 10⁻¹⁸ Joules because the electron dropped from an energy level i to the ground state by emitting a single photon.
Read more on photons here: brainly.com/question/9655595
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Earth's atmosphere blocks many types of light including gamma, x-rays most ultraviolet and infrared. So optical telescopes that use visible light and ultraviolet telescopes that are used to study very hot stars are much less effective on Earth.
To find the answer, take 55 and divide it by 1.85 to get the thickness of one card. In this case the answer would be 29.72973 cm. each.