Posted by **stephen** on Saturday, January 1, 2011 at 6:23pm.

A baseball player hits a line drive to center field. As he rounds second base, he heads directly for third, running at 20 ft/sec. How fast is the distance from the rnner to home plate changing when he is halfway to third base?

- hang on -
**Damon**, Saturday, January 1, 2011 at 6:31pm
aargh, did this yesterday, going to look

- math -
**bobpursley**, Saturday, January 1, 2011 at 6:34pm
http://www.jiskha.com/search/index.cgi?query=A+baseball+player+hits+a+line+drive+to+center+field.+As+he+rounds+second+base%2C+he+heads+directly+for+third%2C+running+at+20+ft%2Fsec.+How+fast+is+the+distance+from+the+rnner+to+home+plate+changing+when+he+is+halfway+to+third+base%3F+

- oh well, did it again -
**Damon**, Saturday, January 1, 2011 at 6:37pm
h^2 = 90^2 + x^2

h is hypotenuse

x is distance from third

where x = (45-20t) so dx/dt = -20

2 h dh/dt = 2 x dx/dt

dh/dt = (x/h) (-20)

at t = 0, x = 45 and h = 100.6

so

dh/dt = -8.94

- Thanks Bob - I did it differently yesterday, same answer -
**Damon**, Saturday, January 1, 2011 at 6:41pm
http://www.jiskha.com/display.cgi?id=1293827209

- math -
**Damon**, Saturday, January 1, 2011 at 6:42pm
x^2 = (45-20*t)^2 + 90^2

2 x dx/dt = 2 *(45-20t) (-20)

at x=sqrt(45^2+90^2) when t = 0

2 (100.6) dx/dt = 90*-20

dx/dt = -8.94 ft/s

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