78 lines
2.8 KiB
Markdown
78 lines
2.8 KiB
Markdown
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---
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id: af4afb223120f7348cdfc9fd
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title: Map the Debris
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challengeType: 5
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---
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## Description
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<section id='description'>
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Return a new array that transforms the elements' average altitude into their orbital periods (in seconds).
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The array will contain objects in the format <code>{name: 'name', avgAlt: avgAlt}</code>.
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You can read about orbital periods <a href="http://en.wikipedia.org/wiki/Orbital_period" target='_blank'>on Wikipedia</a>.
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The values should be rounded to the nearest whole number. The body being orbited is Earth.
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The radius of the earth is 6367.4447 kilometers, and the GM value of earth is 398600.4418 km<sup>3</sup>s<sup>-2</sup>.
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Remember to use <a href='http://forum.freecodecamp.org/t/how-to-get-help-when-you-are-stuck/19514' target='_blank'>Read-Search-Ask</a> if you get stuck. Try to pair program. Write your own code.
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</section>
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## Instructions
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<section id='instructions'>
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</section>
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## Tests
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<section id='tests'>
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```yml
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- text: '<code>orbitalPeriod([{name : "sputnik", avgAlt : 35873.5553}])</code> should return <code>[{name: "sputnik", orbitalPeriod: 86400}]</code>.'
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testString: 'assert.deepEqual(orbitalPeriod([{name : "sputnik", avgAlt : 35873.5553}]), [{name: "sputnik", orbitalPeriod: 86400}], "<code>orbitalPeriod([{name : "sputnik", avgAlt : 35873.5553}])</code> should return <code>[{name: "sputnik", orbitalPeriod: 86400}]</code>.");'
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- text: '<code>orbitalPeriod([{name: "iss", avgAlt: 413.6}, {name: "hubble", avgAlt: 556.7}, {name: "moon", avgAlt: 378632.553}])</code> should return <code>[{name : "iss", orbitalPeriod: 5557}, {name: "hubble", orbitalPeriod: 5734}, {name: "moon", orbitalPeriod: 2377399}]</code>.'
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testString: 'assert.deepEqual(orbitalPeriod([{name: "iss", avgAlt: 413.6}, {name: "hubble", avgAlt: 556.7}, {name: "moon", avgAlt: 378632.553}]), [{name : "iss", orbitalPeriod: 5557}, {name: "hubble", orbitalPeriod: 5734}, {name: "moon", orbitalPeriod: 2377399}], "<code>orbitalPeriod([{name: "iss", avgAlt: 413.6}, {name: "hubble", avgAlt: 556.7}, {name: "moon", avgAlt: 378632.553}])</code> should return <code>[{name : "iss", orbitalPeriod: 5557}, {name: "hubble", orbitalPeriod: 5734}, {name: "moon", orbitalPeriod: 2377399}]</code>.");'
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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function orbitalPeriod(arr) {
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var GM = 398600.4418;
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var earthRadius = 6367.4447;
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return arr;
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}
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orbitalPeriod([{name : "sputnik", avgAlt : 35873.5553}]);
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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function orbitalPeriod(arr) {
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var GM = 398600.4418;
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var earthRadius = 6367.4447;
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var TAU = 2 * Math.PI;
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return arr.map(function(obj) {
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return {
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name: obj.name,
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orbitalPeriod: Math.round(TAU * Math.sqrt(Math.pow(obj.avgAlt+earthRadius, 3)/GM))
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};
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});
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}
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orbitalPeriod([{name : "sputkin", avgAlt : 35873.5553}]);
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```
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</section>
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