Minimum frictional force when F=0??

This the the question.
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Is it true that F=0?

1 Answer
Mar 11, 2018

# F = (m g)/sin theta#

Explanation:

While the the block is not moving

#vec 0 = vec F + vec f + vec P+vec N#

with

#vec F = F(cos theta, sin theta)#
#vec P = m g(0,-1)#
#vec N = (m g - F sin theta)(0,1)#
#vec f = mu_s (m g - F sin theta)(-1,0)# if #m g - F sin theta > 0# otherwise #vec f = vec 0#

then the minimum static friction force #abs (vec f)# is at

#m g - F sin theta = 0 rArr F = (m g)/sin theta#