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shellshock92
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Homework Statement
The static friction between the two blocks is .47 and kinetic friction between the block with mass 9.4 kg and the horizontal surface is 0.21.The acceleration of gravity is 9.8 m/s^2 What is the minimum force F which must be exerted on the 9.4 kg block in order that the 0.8 kg block does not fall? Answer in units of N
diagram: attached
Homework Equations
ƩF=m*a
Fμ = μ*Fn
The Attempt at a Solution
Free Body Diagram: attached
F(net on big block) = F - (.21*m*g)
F(net on small block) = F - (.47*m*a)
Now I made an assumption that F(net on big block) = F(net on small block)
F - (.47*m*a) = F - (.21*m*g)
0 = - (.21*9.4*9.8) + .47*(.8)*a
19.3452 = .376a ... a = 51.45 m/s^2 ?
F(net on small block) = m*a - (.47*m*a) = (.8*51.45) - (.47*.8*51.45) = 21.815 N
I went through this with a TA who told me we could make that assumption, but seeing I got the answer wrong I am quite confused at this point :( Is my approach somewhat correct? I do believe this is the right section to post this if it isn't I am sorry! this problem has been giving me an headache for quite sometime some clarification would be welcomed :)