A 4.04 kg particle has the xy coordinates (-1.24 m, 0.498 m), and a 3.86 kg particle has the xy coordinates (0.399 m, -0.641 m). Both lie on a horizontal plane. At what (a) x and (b) y coordinates must you place a 2.09 kg particle such that the center of mass of the three-particle system has the coordinates (-0.840 m, -0.910 m)?
given
m1 = 4.04 kg at (-1.24 m, 0.498 m) = ( x1 , y1 )
m2 = 3.86 kg at (0.399 m, -0.641 m) = ( x2 , y2 )
m3 = 2.09 kg at (-0.840 m, -0.910 m) = ( xcm , ycm )
a )
xcm = m1 x1 + m2 x2 + m3 x3 / ( m1 + m2 + m3 )
-0.84 = 4.04 X ( -1.24 ) + 3.86 X (0.399 ) + 2.09 X x3 / ( 4.04 + 3.86 + 2.09 )
-0.84 = 4.04 X ( -1.24 ) + 3.86 X (0.399 ) + 2.09 X x3 / ( 9.99 )
- 8.39 = - 5 + 1.54 + 2.09 X x3
2.09 X x3 = - 11.85
x3 = - 5.66 m
b )
same way for
ycm = m1y1 + m2 y2 + m3 y3 / ( m1 + m2 + m3 )
-0.91 = 4.04 X ( 0.498 ) + 3.86 X (-0.641 ) + 2.09 X y3 / ( 4.04 + 3.86 + 2.09 )
-0.91 = 4.04 X ( 0.498 ) + 3.86 X (-0.641 ) + 2.09 X y3 / ( 9.99 )
- 9.09 = 2.011 - 2.41 + 2.09 X y3
2.09 X y3 = - 8.691
y3 = - 4.158 m
finally ( x3 , y3 ) = ( - 5.66 , - 4.158 )
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