Answer: Katherine Johnson's knowledge of (mathematics) was instrumental in the return of the Apollo astronauts from the Moon to Earth.
the answer is C. It allows citizens to submit anonymous tips to the police.
All machines are not 100% efficient because of <span>C. Friction</span>
The intensity on a screen 20 ft from the light will be 0.125-foot candles.
<h3>What is the distance?</h3>
Distance is a numerical representation of the length between two objects or locations.
The intensity I of light varies inversely as the square of the distance D from the source;
I∝(1/D²)
The ratio of the intensity of the two cases;
![\rm \frac{I_1}{I_2} =(\frac{D_2}{D_1} )^2\\\\ \rm \frac{2}{I_2} =(\frac{20}{5} )^2\\\\ \frac{2}{I_2} =4^2 \\\\ I_2= \frac{2}{16} \\\\ I_2= 0.125 \ foot-candles](https://tex.z-dn.net/?f=%5Crm%20%5Cfrac%7BI_1%7D%7BI_2%7D%20%3D%28%5Cfrac%7BD_2%7D%7BD_1%7D%20%29%5E2%5C%5C%5C%5C%20%5Crm%20%5Cfrac%7B2%7D%7BI_2%7D%20%3D%28%5Cfrac%7B20%7D%7B5%7D%20%29%5E2%5C%5C%5C%5C%20%5Cfrac%7B2%7D%7BI_2%7D%20%3D4%5E2%20%5C%5C%5C%5C%20I_2%3D%20%5Cfrac%7B2%7D%7B16%7D%20%5C%5C%5C%5C%20%20I_2%3D%200.125%20%5C%20foot-candles)
Hence, the intensity on a screen 20 ft from the light will be 0.125 foot-candles
To learn more about the distance refer to the link;
brainly.com/question/26711747
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