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Net Torqueby spidey12
Tags: torque 
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#1
Jul2308, 04:04 PM

P: 37

1. The problem statement, all variables and given/known data
The drawing shows a person (weight W = 581 N, L1 = 0.829 m, L2 = 0.399 m) doing pushups. Find the normal force exerted by the floor on each hand and each foot, assuming that the person holds this position. 2. Relevant equations I know this has something to do with net torque. Wd=wd 3. The attempt at a solution Ok i tried figuring this out in sveral ways. first, i tried multiplying L1 with 581, the persons weight, and then i divided by 2. This did not work. so tried multplying times l1+l2 and that did not work either. What am I doing wrong? i was sure i had it right the first time around. 


#2
Jul2308, 04:44 PM

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P: 5,343

You could treat it as a torque problem then with there being no torque about what convenient point? You look like you have enough knowns to give you an answer. 


#3
Jul2308, 05:20 PM

P: 37

also i tried adding the two lengths together and just getting the midpoint and multiplying that times the Weight but I do not think this is correct. 


#4
Jul2308, 05:41 PM

HW Helper
P: 5,343

Net Torque
Let [tex]W_T_O_T = W_H_A_N_D_S + W_F_E_E_T[/tex] If it is balanced then: [tex]W_H_A_N_D_S * L_2 = W_F_E_E_T * L_1[/tex] All you have to do is solve. (Remember they want the answer for EACH hand and foot. Just divide those answers by 2.) 


#5
Jul2308, 06:46 PM

P: 37

Ok i already had that equation but i dumped it because there is not unknown...we know l1 and l2, we know the weight of the hands and feet (both are 581)..so what am i solving for? 


#6
Jul2308, 08:19 PM

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P: 5,343

They all add to the TOTAL weight, yes that is given, but what is the weight on each? How is that weight DISTRIBUTED. That is what you were asked. 


#7
Jul2308, 09:08 PM

P: 37

But right now i have an equation in which i have four variables and i already know ALL FOUR variables. What am i solving for? 


#8
Jul2308, 09:55 PM

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P: 5,343

[tex]W_F_E_E_T = ?[/tex] Because trust me [tex]W_H_A_N_D_S[/tex] is NOT equal to [tex]W_F_E_E_T[/tex] All you know is that they add to 581N. How that weight is distributed by solving for them using the 2 equations is what the problem wants. And yes [tex]W_H_A_N_D = 1/2 *W_H_A_N_D_S[/tex] and [tex]W_F_O_O_T = 1/2 * W_F_E_E_T[/tex] but they are not all equal to each other. 


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