What is the speed of the 130 g ball?

Question

A 130 g ball and a 210 g ball are connected by a 40-cm-long, massless, rigid rod. The balls rotate about their center of mass at 140 rpm.

1) What is the speed of the 130 g ball?

Answer 1

the center of mass will be the point where the end mass x the distance from the center of mass are equal

130 D = 210 (40 - D)

130D = 8400  - 210D

340D = 8400

D = 24.7 cm

the 130 g ball effectively moves is a circle with a radius of 24.7 CM

circumference  = 24.7 x 2 x3.14 = 155.12 cm

155.12 x 140 rpm= 21,716.8 cm/minute

21.716.8/60 = 361.95 cm/s