Need some help with this one! can\'t figure it out at all! thanks so much! As sh

Question

Need some help with this one! can't figure it out at all! thanks so much!

As shown on the right, a small disk m1 = 100. grams is sliding frictionlessly across a horizontal table top at 10.0 m/s when it runs into and sticks to an initially stationary second small disk m2 = 200. grams. The second disk is attached to a frictionless piviot (P) by a thin steel wire of length 50.0 cm and 1 00 mm diameter. After the collision, the two small masses continue to move together in a circular path on the table top and careful measurements show that the wire is now slightly longer than it was before the collision. How much longer is it? Given: Y steel = 180. GPa

Explanation / Answer

m1 * v1 = ( m1+ m2 ) * v2

final velocity of two discs = 10/3 m/sec

final mass of asembly = 300 gm

tension in rod = 0.3 * (10/3)^2 / 0.5

= 6.6667 N

so, stress = 6.6667 / ( pi * (0.001^2) / 4 )

= 8.488 Mpa

strain = 8.488 * 10^6 / 180 * 10^9 = 4.716 * 10^-5

so,

elongation = 4.716 * 10^-5 * 50 = 0.00236 cm longer

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