This preview shows pages 1–10. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: PHYSICS 231 INTRODUCTORY PHYSICS I Lecture 8 • Work for nonconstant force • Spring force • Potential Energy of Spring • Power Last Lecture F = κξ PE = 1 2 κξ 2 P = D W D t = D KE D t P = Fv F x Chapter 6 Momentum and Collisions Momentum Definition: Newton’s 2 nd Law: r p = μ ρ ω ρ F = m D r v D t ρ F = D r p D t Conservation of Momentum True for isolated particles (no external forces) Proof: Recall F 12 =F 21 , (Newton’s 3 rd Law) for isolated particles never changes! ρ F 12 + r F 21 = 0 D r p 1 D t + D r p 2 D t = 0 r ∆ ρ p 1 + D r p 2 = 0 r p 1 f + r p 2 f = r p 1 i + r p 2 i ρ p i Momentum is a Vector quantity • Both Σ p x and Σ p y are conserved p x = μ ω ξ π ψ = μ ω ψ Example 6.1 An astronaut of mass 80 kg pushes away from a space station by throwing a 0.75kg wrench which moves with a velocity of 24 m/s relative to the original frame of the astronaut. What is the astronaut’s recoil speed? 0.225 m/s Center of mass does not accelerate X cm μ 1 ξ 1 + μ 2 ξ 2 + μ 3 ξ 3 + ... (μ 1 + μ 2 + μ 3 + ...29 ∆ X cm = m 1 D x 1 + m 2 D x 2 + m 3 D x 3 + ... ( m 1 + m 2 + m 3 + ...) = D t m 1 (D x 1 / D t ) + m 2 (D x 2 / D t ) + m 3 (D x 3 / D t ) + ... ( m 1 + m 2 + m 3 + ...) = D t p 1 + p 2 + p 3 + ... ( m 1 + m 2 + m 3 + ...) = 0 if total P iszero Example 6.2 Ted and his iceboat (combined mass = 240 kg) rest on the frictionless surface of a frozen lake. A heavy rope (mass of 80 kg and length of 100 m) is laid out in a line along the top of the lake. Initially, Ted and the rope are at rest. At time t=0, Ted turns on a wench which winds 0.5 m of rope onto the boat every second....
View
Full
Document
This note was uploaded on 07/25/2008 for the course PHY 231 taught by Professor Smith during the Spring '08 term at Michigan State University.
 Spring '08
 smith
 Physics, Energy, Force, Momentum, Potential Energy, Power, Work

Click to edit the document details