math
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