Ch9 HW3 S2008

# Ch9 HW3 S2008 - Ch9 HW3 S2008 10:33 AM Web Assign Ch9 HW3...

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4/25/08 10:33 AM Ch9 HW3 S2008 Page 1 of 8 http://www.webassign.net/[email protected]/[email protected] Ch9 HW3 S2008 (Homework) KRISTIN SEILOFF Instructor: Jennifer Curtis Description Momentum and energy in collisions: Unequal masses; 2D collisions Instructions Reading: CH9 Web Assign Current Score: 51 out of 55 Due: Friday, March 28, 200808:35 AM EDT 1. 9/9 points In outer space rock 1, with mass 6 kg and velocity < 3900 , -3200 , 2800 > m/s, struck rock 2, which was at rest. After the collision, rock 1's velocity is < 3500 , -2500 , 3300 > m/s. What is the final momentum of rock 2? 2 f = < 2400 2400 , -4200 -4200 , -3000 -3000 > kg · m/s Before the collision, what was the kinetic energy of rock 1? K 1 i = 99870000 9.99e+07 J Before the collision, what was the kinetic energy of rock 2? K 2 i = 0 0 J After the collision, what is the kinetic energy of rock 1? K 1 f = 88170000 8.82e+07 J Suppose the collision was elastic (that is, no change in kinetic energy and therefore no change in thermal or other internal energy of the rocks). In that case, after the collision, what is the kinetic energy of rock 2? K 2 f = 11700000 1.17e+07 J On the other hand, suppose that in the collision some of the kinetic energy is converted into thermal energy of the two rocks, where E thermal,1 + E thermal,2 = 7.02 10 6 J. What is the final kinetic energy of rock 2?

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4/25/08 10:33 AM Ch9 HW3 S2008 Page 2 of 8 http://www.webassign.net/[email protected]/[email protected] K 2 f = 4680000 4.68e+06 J In this case (some of the kinetic energy being converted to thermal energy), what was the transfer of energy Q (microscopic work) from the surroundings into the two-rock system during the collision? (Remember that Q represents energy transfer due to a temperature difference between a system and its surroundings.) Q = 0 0 J Solution or Explanation sys = net t = 0, so the momentum of the system doesn't change. Therefore, 1f + 2f = sys,i If the collision was elastic then K 1f + K 2f = K sys,i If some kinetic energy is converted into the thermal energy of the two rocks, then K 1f + K 2f + E thermal, sys = K sys,i Although the system's temperature rises (associated with the increase in its internal or thermal energy), in the rapid collision there isn't time for any significant thermal energy transfer Q to the cooler surroundings. Eventually the system will cool down as a result of thermal energy transfer to the surroundings, but this will take a while. 2. 22/22 points
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Ch9 HW3 S2008 - Ch9 HW3 S2008 10:33 AM Web Assign Ch9 HW3...

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