Algebra.Com's Answer #407789 by Edwin McCravy(20056)![\"\"](\"/images/stars/stars-13.gif\")  
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document.write( "a rocket weighs 6000 pounds when it is resting on the launch pad. the engines burn fuel at the rate of 20 pounds per second.\r
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document.write( " a. write a linear function W(t) expressing rocket weigh as a function of time t in seconds
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document.write( "Let x = t
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document.write( "Let y = W(t) \r
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document.write( "When x = 0, y = 6000
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document.write( "When x = 1, y = 5980, because it lost 20 pounds in 1 second\r
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document.write( "The problem now becomes the problem:\r
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document.write( "Find the equation of the line through the points (0,6000) and (1,5980)\r
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document.write( "1. find an equation of the line passing through the points \r\n" );
document.write( "(0, 6000) and (1, 5980)\r\n" );
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document.write( "Slope formula\r\n" );
document.write( "m =  with (x1, y1) = (0,6000) and (x2, y2) = (1, 5980)\r\n" );
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document.write( "m =  =  = -20 \r\n" );
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document.write( "Point-slope formula:\r\n" );
document.write( "y - y1 = m(x - x1)\r\n" );
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document.write( "y - 6000 = -20(x - 0)\r\n" );
document.write( "y - 6000 = -20x\r\n" );
document.write( "y = -20x + 6000\r\n" );
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document.write( "Now change y back to W(t) and x back to t\r\n" );
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document.write( "W(t) = -20t + 6000 \r\n" );
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document.write( "-------------------------------------------\r\n" );
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document.write( " b. at what time into the launch will the rocket weigh 40% of its original weight ?\r\n" );
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document.write( "40% of 6000 is 0.4(6000) = 2400\r\n" );
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document.write( "We want to know t when W(t) = 2400, so we substitute\r\n" );
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document.write( "2400 for W(t) in\r\n" );
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document.write( "W(t) = -20t + 6000 \r\n" );
document.write( "2400 = -20t + 6000\r\n" );
document.write( " 20t = 3600\r\n" );
document.write( " t = 180 seconds or 3 minutes.\r\n" );
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document.write( "Edwin \n" );
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