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Homework 7 - Physics 131

# Homework 7 - Physics 131 - Homework 7 Physics 131...

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PHYSICS 131 (http://www.google.com/) Search HOMEWORK 7 A One-Dimensional Inelastic Collision Find the magnitude p_i of the total initial momentum of the two-block system. p_i = m1v1+m2v2 (v2=0) p_i = m1v1 Find v_f, the magnitude of the final velocity of the two-block system. p_i = p_f m1v1+m2v2 = m1v_f1+m2v_f2 (v2=0) m1v1 = (m1+m2)v_f v_f = (m1v1)/(m1+m2) What is the change deltaK = K_f-K_i in the system's kinetic energy due to collision? deltaK = [(1/2)m1(v_f1^2) + (1/2)m2(v_f2^2)] - [(1/2)m1(v1^2) + (1/2)m2(v2^2)] (v2=0 and v_f1 = v_f2) deltaK = [(1/2)(m1+m2)(v_f^2)] - [(1/2)m1(v1^2)] *Note : Answer is negative Problem 9.9 What is the mass of the second car? p_i = p_f m1v1+m2v2 = m1v_f1+m2v_f2 (v2=0 and v_f1=v_f2) m1v1 = (m1+m2)v_f m2 = [(m1v1)/v_f] - m1 Homework 7 - Physics 131 http://physics131.webs.com/homework7.htm 1 of 8 12/21/10 8:51 PM

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A Bullet Is Fired into a Wooden Block Which of the following best describes this collision? Perfectly Inelastic (Pefectly Elastic: No loss of Kinetic Energy, Partially Inelastic: Loss of Kinetic Energy but objects don't stick, Perfectly Inelastic: Loss of Kinetic Energy and objects stick) Which of the following quantities, if any, are conserved during this collission? Momentum Only (Remember: Momentum is always conserved regardless of being an elastic or inelastic collision is there is no external force) What is the speed of the block/bullet system after the collission? mbvb+mw vw = mbv_fb+mw v_fw (vw=0, v_fb=v_fw and vb=vi) mbvi = (mb+mw)v_f v_f = (mbvi)/(mb+mw) Problem 9.13 Calculate the velocity of the boat immediately after. m1v1+m2v2 = m1v_f1+m2v_f2 (v1=v2=0 ,since everything is initially at rest) 0 = m1v_f1+m2v_f2 v_f2 = -((m1v1)/m2) ,where m1=mass of package and m2=mass of child and boat combined *Note: The answer is negative since the child and boat move in the negative x-axis Problem 9.35 Assuming a perfectly elastic collision, what will be the speed of each object after the collision? Since kinetic energy is conserved in elastic collision.
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Homework 7 - Physics 131 - Homework 7 Physics 131...

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