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ansmid3

# ansmid3 - Name Physics 121 Dr Callahan Summer I 2008...

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Name: Physics 121, Dr. Callahan Summer I 2008, Midterm #3 Note: Show your work. Clarity counts. You may use one 8 1 2 × 11 sheet of notes (both sides) and a calculator. 1 2 3 1. A 3.4 kg mass moving north at 1 . 5 m / s hits and sticks to a 5.0 kg mass moving southwest (45 west of south) at 2 . 3 m / s. The collision is completely inelastic. Find the magnitude and direction of the final velocity of the combined masses. Answer: Let x point east and y point north. The x - and y -components of momentum are conserved. Thus m 1 v 10 x + m 2 v 20 x = ( m 1 + m 2 ) v fx , so v fx = m 1 v 10 x + m 2 v 20 x m 1 + m 2 = (3 . 4 kg)(0 m / s) - (5 . 0 kg)(2 . 3 m / s) sin 45 (3 . 4 kg) + (5 . 0 kg) = - 0 . 97 m / s . Similarly, m 1 v 10 y + m 2 v 20 y = ( m 1 + m 2 ) v fy , so v fy = m 1 v 10 y + m 2 v 20 y m 1 + m 2 = (3 . 4 kg)(1 . 5 m / s) - (5 . 0 kg)(2 . 3 m / s) cos 45 (3 . 4 kg) + (5 . 0 kg) = - 0 . 36 m / s . Thus v f = radicalBig v 2 fx + v 2 fy = 1 . 0 m / s , θ = Tan - 1 parenleftbigg v fy v fx parenrightbigg = 20 south of west. 2. Consider a uniform stick of mass m and length L , attached at one end to the floor by a hinge, so that it is free to pivot about that end. The stick starts out motionless and nearly vertical, then gravity pulls

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ansmid3 - Name Physics 121 Dr Callahan Summer I 2008...

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