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Physics 1a, Section 2

Physics 1a, Section 2. October 21, 2010. Second Quiz. covers: Frautschi chapters 4 - 8.4 (and 1 - 3) lectures/sections through yesterday (Oct. 20) homework #2-3 (and #1). Quiz Problem 37. Quiz Problem 37. Answer: N = m w 2 R, cos q = g/( w 2 R) r = (R 2 – g 2 / w 4 ) 1/2

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Physics 1a, Section 2

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  1. Physics 1a, Section 2 October 21, 2010

  2. Second Quiz • covers: • Frautschi chapters 4 - 8.4 (and 1 - 3) • lectures/sections through yesterday (Oct. 20) • homework #2-3 (and #1)

  3. Quiz Problem 37

  4. Quiz Problem 37 • Answer: • N = mw2R, cosq = g/(w2R) • r = (R2 – g2/w4)1/2 • When w <= (g/R)1/2, marble sits on bottom of bowl

  5. Problem Solving Hints:Normal Force and Friction • suggested order: 1) draw gravity and other fixed external forces (direction and magnitude are unambiguous) 2) draw normal force (prevents interpenetration of objects) 3) draw friction force (perpendicular to normal force) • kinetic friction: F = mkN direction opposite to relative velocity • static friction: F ≤ msN direction and magnitude to prevent relative acceleration

  6. Quiz Problem 48:kinetic friction

  7. Quiz Problem 48 • Answer: • m1a = T + m1g(sinq – m1cosq), m2a = -T + m2g(sinq – m2cosq) • a = g[sinq – cosq(m1m1+m2m2)/(m1+m2)], T = gcosq(m1-m2)m1m2/(m1+m2) • m1 > m2

  8. Quiz Problem 11: static & kinetic friction

  9. Quiz Problem 11 • Answer: • a = g(m1scosq - sinq) • F = (m1+m2)g(m2k + m1s)cosq

  10. Monday, October 25: • Quiz Problem 29 (non-inertial frames) • Quiz Problem 49 (springs) • Optional, but helpful, to try these in advance.

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