document.write( "Question 1099374: Suppose an object is thrown from a platform that is 300 ft. above the Earth with a beginning velocity of +7 ft/sec. How fast is it going at t = 2 seconds? \r
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Algebra.Com's Answer #713844 by KMST(5328)\"\" \"About 
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The acceleration of gravity (anywhere you can stand on Earth) is \"32\"\"ft%2Fs%5E2\" in magnitude (absolute value).
\n" ); document.write( "That is the number to use in physics problems.
\n" ); document.write( "A beginning velocity of +7 ft/s means nothing,
\n" ); document.write( "until we agree on which direction we use for positive distances, velocities, and accelerations.
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\n" ); document.write( "If the object was thrown up,
\n" ); document.write( "a starting velocity of +7 ft/s means 7 ft/s in an upwards direction,
\n" ); document.write( "and everything upwards is positive, downwards is negative.
\n" ); document.write( "Then, acceleration is \"-32\"\"ft%2Fs%5E2\"
\n" ); document.write( "velocity (in ft/s) as a function of \"t\" (time in seconds since the object was released) will be
\n" ); document.write( "\"v%28t%29=7-32t\" until the object hits the ground,
\n" ); document.write( "and at \"t=2\" , assuming the object has not hit the ground,
\n" ); document.write( "\"v%282%29=7-32%2A2=7-64=-57\" .
\n" ); document.write( "At t=2 seconds, the object is moving downwards, at 57 ft/s .
\n" ); document.write( "It obviously has not hit the ground yet, because even going at \"v%282%29\" for the full 2 seconds, it would not have covered the 300 ft distance.
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\n" ); document.write( "If the object was thrown down,
\n" ); document.write( "a starting velocity of +7 ft/s means 7 ft/s in an downwards direction,
\n" ); document.write( "and everything downwards is positive, upwards is negative.
\n" ); document.write( "Then, acceleration is \"32\"\"ft%2Fs%5E2\"
\n" ); document.write( "velocity (in ft/s) as a function of \"t\" (time in seconds since the object was released) will be
\n" ); document.write( "\"v%28t%29=7%2B32t\" until the object hits the ground,
\n" ); document.write( "and at \"t=2\" , assuming the object has not hit the ground,
\n" ); document.write( "\"v%282%29=7%2B32%2A2=7%2B64=61\" .
\n" ); document.write( "At t=2 seconds, the object is moving downwards, at 61 ft/s .
\n" ); document.write( "It obviously has not hit the ground yet, because even going at \"v%282%29\" for the full 2 seconds, it would not have covered the 300 ft distance.
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\n" ); document.write( "NOTE:
\n" ); document.write( "The height of the platform is useful only to figure out when the object will hit the ground.
\n" ); document.write( "Height in feet above the ground will be
\n" ); document.write( "\"h%28t%29=-16t%5E2+%2B-+7t+%2B300\" , with the \"%22+%22+%2B-+%22+%22\" covering the thrown upwards or downwards possibilities,
\n" ); document.write( "and the object will hit the ground at \"t=4.6\" or \"t=4.1\" ,
\n" ); document.write( "also depending on whether it was thrown upwards or downwards.
\n" ); document.write( "The apparent downwards acceleration on a falling object will be slightly less on the Equator,
\n" ); document.write( "and slightly more on the poles,
\n" ); document.write( "but thosee differences are very small,
\n" ); document.write( "and the theoretical/calculated difference from starting on or 300 ft above Earth's surface is much, much, much smaller.
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