Posted by anna on Thursday, November 4, 2010 at 9:26pm.
this is basically the diagram to my question
A person of mass m = 62 kg is doing push-ups as shown in the attached figure. The distances are a = 91 cm and b = 60% of l1. Calculate the vertical component of the normal force exerted by the floor on both hands.
Can someone please explain this problem to me i don't know how to approach it..i understand that i will have to use times each distance by the weight but i don't understand what to do next?
physics - bobpursley, Thursday, November 4, 2010 at 9:41pm
I cant load the site, I will try later. The idea is that you sum moments (clockwise+, counterclockwise-) and set equal to zero. A moment is Force*distance*sinAnglebetweenthem(usually 90 degrees).
physics - Anonymous, Thursday, November 4, 2010 at 9:44pm
y-direction: N1 + N2 - Fg = 0
x-direction: L1 x N1 - L2 x N2 = 0
Fg = mg
physics - anna, Thursday, November 4, 2010 at 9:55pm
you just have to add w w w to the website
physics - anna, Thursday, November 4, 2010 at 9:57pm
can u explain to me what you mean by y direction is equal to and for the force *distance *the angle i don't know the angle for the question
physics - Anonymous, Thursday, November 4, 2010 at 10:02pm
Since we're only trying to find the Normal Force exerted by the two hands, we automatically assume that it's in mechanical equilibrium, thus equaling to zero.
physics - anna, Thursday, November 4, 2010 at 10:03pm
okay but can you explain to me how to find N1 and N2
Anonymous and bobpursley - anna, Thursday, November 4, 2010 at 10:09pm
can you please Anonymous and bobpursley explain this to me.
Please and thank you
physics - Anonymous, Thursday, November 4, 2010 at 11:23pm
isolate N1 for the first eq:
N1 = Fg - N2
N1 x L1 - N2 x L2 = 0
sub N1 from eq 1 to eq 2.
(Fg - N2)L2 - N2 x L2=0
(Fg - N2 x L2) - N2 x L2 = 0
Fg = N2 x L2 + N2 x L1
Fg = N2(L2+L1)
since we already know Fg = mg, we isolate for N2
N2 = Fg/(L2+L1)
Thus the normal for N2 is found. Now look back to eq 1 again:
N1 + N2 - Fg = 0
then isolate for N1 by substituting the found value N2.
Make sure you convert cm to m.
physics - Anonymous, Thursday, November 4, 2010 at 11:25pm
Once the N1 is found, add the to Normal forces and voila!
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