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A barbell consists of a 500g ball and a 2.0 Kg ball connected by a massless 50-c

ID: 1562014 • Letter: A

Question

A barbell consists of a 500g ball and a 2.0 Kg ball connected by a massless 50-cm-long rod Where is the center of mass X_cm with respect to the center of the heavier mass m_1? (a) 0.50 m (b) 0.40 m (c) 0.30 m (d) 0.20 m (e) 0.10 m (f) none of these What is the speed of the 2.0-Kg ball if they rotate about the center of mass at 40 rpm? (a) 41.9 m/s (b) 1.76 m/s (c) 0.42 m/s (d) 0.04 m/s (e) none of these What is the speed of the 500-g ball if they rotate about the center of mass at 40 rpm? (a) 10.5 m/s (b) 7.02 m/s (c) 1.68 m/s (d) 0.67 m/s (e) none of these

Explanation / Answer

let m1 = 2 kg, m2 = 0.5 kg

x1 = 0, x2 = 0.5 m

5) e) 0.1 m

Xcm = (m1*x1 + m2*x2)/(m1+m2)

= (2*0 + 0.5*0.5)/(2 + 0.5)

= 0.1 m

6) c) 0.42 m/s

w = 40 rpm

= 40*2*pi/60 rad/s

= 4.19 rad/s

v1 = r2*w

= 0.1*4.19

= 0.42 m/s

7) c) 1.68 m/s

v2 = r2*w

= 0.4*4.19

= 1.68 m/s

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