
#1
Oct1406, 08:52 PM

P: 191

A crate of mass 11.0 kg is pulled up a rough incline with an initial speed of 1.50 m/s. The pulling force is 100 N parallel to the incline, which makes an angle of 16.5° with the horizontal. The coefficient of kinetic friction is 0.400, and the crate is pulled 5.65 m.
(b) How much mechanical energy is lost due to friction? well, this is what i came up with to find the energy lost i thought F  f so to find f = u_kN N = (mgsin16.5) f = .400(30.62) f = 12.25 100  12.25 = 87.75 is incorrect what am i doing wrong? 



#2
Oct1406, 09:33 PM

Sci Advisor
HW Helper
P: 6,559

The energy lost is the work added by the pulling force less the work done by the friction force. AM 



#3
Oct1506, 01:48 AM

P: 191

I dont understand what you mean. The teacher decided to skip most of the stuff on this chapter and basically i am learning this on my own and from the book i got to read which i dont understand from the reading.




#4
Oct1506, 02:10 AM

P: 186

energy lost due to friction
Energy loss is simply Kinetic friction multiply by the distance travelled. To find kinetic friction, take coefficient of friction multiply by normal force acting on the block. Is the answer 23.8J? I'm not sure if i'm right also.




#5
Oct1506, 02:13 AM

P: 191

that answer is incorrect.
work done by gravity is 172.99 



#6
Oct1506, 02:24 AM

P: 186

wat is the answer?




#7
Oct1506, 02:25 AM

P: 191

the book doesnt give an answer because its an even # problem, which doesnt help me at all since i cant use any other answer to figure this one out since this is the only problem in the book that ask this.
forgot to mention this is also on an online homework I have that is how I know i been getting the wrong answer. oh yea i mention work done by gravity because that was the first part of the problem i needed to find and thought maybe i need to use that somehow. 



#8
Oct1506, 02:27 AM

P: 186

then how u know that ur answer is wrong?




#9
Oct1506, 02:31 AM

P: 186

oops. I've forgot to add in the gravitational field strength. Is the answer 233.8J?




#10
Oct1506, 02:32 AM

P: 191

okay, that is the correct answer.
Can you explain how you get that? 



#11
Oct1506, 02:37 AM

P: 186

wats the value for g?




#12
Oct1506, 02:39 AM

P: 191

is g = 9.8?




#13
Oct1506, 02:42 AM

P: 186

so 233.8J is right?




#14
Oct1506, 02:43 AM

P: 191

yea, that is the correct answer




#15
Oct1506, 02:52 AM

P: 186

Alright. Its just the same as how i do it in post #4. To find the energy lost due to friction, u need to take kinetic friction multiply by the distance travelled. The way u calculate normal force is wrong. It should be mgcos16.5 and not mgsin16.5. After calculating the kinetic friction, multiply it by the distance travelled, ie: 5.65 to solve for ur energy loss due to friction.
Dun get lost with the many values given in there. Just do what u need to do according to the formulas. Some of the values in the question are just there to mislead you. You dun necessarily have to use them all everytime. Cheers! 



#16
Oct1506, 02:54 AM

P: 191

ahhhhh.....thanks so much. yea those other number were just there and i thought okay those number have to be there for a reason.




#17
Oct1506, 03:01 AM

P: 186

not a problem.



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