Solutions09 - Physics 140 - Discussion 09 - Solutions 7.19....

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Unformatted text preview: Physics 140 - Discussion 09 - Solutions 7.19. I DENTIFY and S ET UP : Use energy methods. There are changes in both elastic and gravitational potential energy; elastic; 2 1 2 , U kx = gravitational: . U mgy = E XECUTE : (a) 2 1 2 U kx = so 2 2(3 20 J) 0 0632 m 6 32 cm 1600 N/m U x k . = = = . = . (b) Points 1 and 2 in the motion are sketched in Figure 7.19. 1 1 other 2 2 + + = + K U W K U other W = (Only work is that done by gravity and spring force) 1 0, = K 2 K = y = at final position of book 1 ( ), U mg h d = + 2 1 2 2 U kd = Figure 7.19 2 1 2 ( ) mg h d kd + + + = The original gravitational potential energy of the system is converted into potential energy of the compressed spring. 2 1 2 kd mgd mgh-- = 2 1 1 ( ) 4 ( ) 2 = ± + d mg mg k mgh k d must be positive, so ( 29 2 1 ( ) 2 d mg mg kmgh k = + + 2 1 (1 20 kg)(9 80 m/s ) 1600 N/m d = . . + 2 2 2 ((1 20 kg)(9 80 m/s )) 2(1600 N/m)(1 20 kg)(9 80 m/s )(0 80 m) . . + . . ....
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This note was uploaded on 02/15/2012 for the course PHYS 140 taught by Professor Uher during the Winter '10 term at University of Michigan.

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Solutions09 - Physics 140 - Discussion 09 - Solutions 7.19....

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