ch08-p065

ch08-p065 - 65. We observe that the last line of the...

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65. We observe that the last line of the problem indicates that static friction is not to be considered a factor in this problem. The friction force of magnitude f = 4400 N mentioned in the problem is kinetic friction and (as mentioned) is constant (and directed upward), and the thermal energy change associated with it is Δ E th = fd (Eq. 8-31) where d = 3.7 m in part (a) (but will be replaced by x , the spring compression, in part (b)). (a) With W = 0 and the reference level for computing U = mgy set at the top of the (relaxed) spring, Eq. 8-33 leads to UK E v d g f m i =+ ¡ =− F H G I K J Δ th 2 which yields v = 74 .ms for m = 1800 kg. (b) We again utilize Eq. 8-33 (with W = 0), now relating its kinetic energy at the moment it makes contact with the spring to the system energy at the bottom-most point. Using the same reference level for computing U = mgy as we did in part (a), we end up with gravitational potential energy equal to mg (– x ) at that bottom-most point, where the spring (with spring constant k 15 10 5 . N m) is fully compressed.

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This note was uploaded on 05/17/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.

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ch08-p065 - 65. We observe that the last line of the...

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