Conservation Of Energy Problem

  • Thread starter leolaw
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  • #1
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So this is the quaiton that i have problem w/:
A 4kg bundle starts up a 30 degree incline with 128J of kinetic energy. How far willl it slide up the incline if the coefficient of kinetic friction between bundle and incline is 0.3?

Because E_initial + Work = E_final and the Work done in the system in this problem is jsut the fricition force, so I have
128 + [tex]\mu[/tex]F_f = 0
128 - [tex]\mu[/tex]mg cos [tex]\theta[/tex] d = 0

since that d is what we are looking for, rearranging this equation gives me:
128 / ([tex]\mu[/tex]mg cos [tex]\theta[/tex]) = d

and d = 12.6m

however, the answer is 4.3m, did I mess up any steps above?
 
Last edited:

Answers and Replies

  • #2
Doc Al
Mentor
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Don't forget that gravity also does work on the object. (Or, alternatively, make sure that energy includes both kinetic and gravitational PE.)
 

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