cement bag forum

Which requires work,lifting 25kg bag of cement 10m vertically in1 min.,or lift a 50kg bag 5m vertically 2min.

Naughtybutt , Sunday, 8th of August 2010 10:48:21 AM

25 kg bag
50 kg bag
both
 
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love bunny , Monday, 9th of August 2010 08:59:50 PM

25 x 10 = 250.  
love bunny
50 x 5 = 250.  
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Both require the same effort input. The effort required to lift the 50kg  
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bag is just spread out over 2 mins.  
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Flirtz , Tuesday, 10th of August 2010 05:48:20 AM

This problem has nothing to do with the time required to do  
Flirtz
it.  
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What work (W) is being performed?  
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A weight is lifted in either case, thereby the potential energy(PE) of the  
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bags is increased:  
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Here it is: W= change in (PE)  
 
Case 1: W = 25 (10-0) = 250 kg-m  
Case 2: W = 50 (5-0) = 250 kg-m  
 
 
 
 
 
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Lily pad , Wednesday, 11th of August 2010 11:21:11 AM

Indeed work = force x distance but in this case he needs to  
Lily pad
account for work over time as well or work/time. Apply the formulas to  
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both situations and the correct answer is the least.  
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Monkey , Thursday, 12th of August 2010 09:16:18 PM

both require work  
Monkey
Work = force x distance  
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Mandy candy , Friday, 13th of August 2010 07:02:20 PM

m1 = 25 kg  
Mandy candy
Δy1 = 10 m  
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t1 = 60 s  
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m2 = 50 kg  
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Δy2 = 5 m  
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t2 = 120 s  
 
Δy = 0.5•a•t^2 => a = 2•Δy/t^2  
F = m•a  
W = F•Δy  
 
a1 = 2•Δy1/t1^2 = 2•10/(60)^2 = 0.0056 m/s^2  
a2 = 2•Δy2/t2^2 = 2•5/(120)^2 = 0.00069 m/s^2  
 
F1 = m1•a1 = 25•0.0056 = 0.14 N  
F2 = m2•a2 = 50•0.00069 = 0.035 N  
 
W1 = F1•Δy1 = 0.14•10 = 1.4 J  
W2 = F2•Δy2 = 0.035•5 = 0.17 J  
 
W1 > W2 so the 25kg bag is more work.  
 
 
 
 
 
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