document.write( "Question 989337: A person of height 1.68 m is walking away from a lamp-post at 1.5 m/s. The light on the lamp-post is 5.3 m above the ground. \r
\n" ); document.write( "\n" ); document.write( "At what rate (in m/s to the nearest cm/s) is the length of the person's shadow changing?\r
\n" ); document.write( "\n" ); document.write( "At what speed (in m/s to the nearest cm/s) is the tip of the person's shadow moving across the ground?\r
\n" ); document.write( "\n" ); document.write( "I'm really stuck\r
\n" ); document.write( "\n" ); document.write( "THANK YOU \n" ); document.write( "
Algebra.Com's Answer #609746 by rothauserc(4718)\"\" \"About 
You can put this solution on YOUR website!
man is p from pole
\n" ); document.write( "shadow tip is s from pole
\n" ); document.write( "we want ds/dt\r
\n" ); document.write( "\n" ); document.write( "s/5.3 = (s-p)/1.68
\n" ); document.write( "(similar triangles)
\n" ); document.write( "1.68 s = 5.3 s - 5.3 p
\n" ); document.write( "3.62 s = 5.3 p
\n" ); document.write( "s = 1.464088398 p approx 1.46 p
\n" ); document.write( "ds/dt = 1.46 dp/dt
\n" ); document.write( "but dp/dt = 1.5
\n" ); document.write( "so
\n" ); document.write( "ds/dt = 2.19 m/s
\n" ); document.write( "this tells us that the length of the person's shadow is changing at the rate of 2.19 m/s
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\n" ); document.write( "the speed (in m/s to the nearest cm/s) that the tip of the person's shadow moving across the ground is 1.5 + 2.19 = 3.69 m/s
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