Question

Minimum frictional force when F=0??

This the the question.

Is it true that F=0?

Answer 1

`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`