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Exam__2_Solutions_F05

Exam__2_Solutions_F05 - Physics 112 Prelim#2 Solutions 1 2...

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Physics 112 - Prelim #2 Solutions Fall 2005 1. (a) -0.1 m & +0.1 m (1 point each) (c) 0.1 m (1 point) (b ) -0.1 m to +0.1 m (2 points) (d) 4.0 J (2 points) 2. C [Skier has KE at the top of the trajectory.] 3. (a) A (2 points) (c) F (3 points, 1 point for E) (b ) D (3 points, 1 point for C) 4. G 5. Down (A B) Up (A B) W by gravity (+20 J) -20 J (-1 for the 1st, 3rd, 5th, W by normal contact force 0 0 and odd nth errors; W by friction (-5 J) -5 J -1 for the 12th error) W by spring -25 J +25 J Δ U gravitational -20 J +20 J Δ U spring +25 J -25 J Δ K block -10 J 0 6. B [CM doesn’t move.] 7. E & G (3 points each, -2 for each additional incorrect answer down to 0 minimum) 8. A [CM follows original path.] 9. (a) F (b) F (c) F (d) T (e) T (f) F (2 points each) 10. (a) 1-D collision: Cons. of x-Momentum: Σ p x = mv o = (m + 2m)v 1 Just after collision: v 1 = v o /3 = (2.0 m/s) = 0.67 m/s Bumper compresses: Cons. of Energy: K 1 + U s1 = K f + U sf 1 2 (3m)v 1 2 + 0 = 0 + 1 2 kx 2 x = 3m k v 1 = 3(1000 kg) 3.2 × 10 4 N/m (0.67 m/s) = 0.20 m (b) Elastic 1-D collision: v Bf = 2m A m B + m A v Ao + m B - m A m B + m A v Bo = 2(1000 kg) 3000 kg (2.0 m/s) + 0 = 1.33 m/s Bumper compresses: Cons. of Energy: K 1 + U s1 = K f + U sf
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1 2 (2m)v 1 2 + 0
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