What is the maximum value of the force F such that the block shown in Fig. 7. 165. does not move ?

Options

A. 20 N
B. 10 N
C. 12 N
D. 15 N

Answer

A

Explanation

F cos `60^(@) = f = mu N " " ….. (i) `
and F sin `60^(@) + mg = N`

From Eqns. (i) and (ii) , F cos `60^(@) = mu [F sin 60^(@) + mg]`

`implies F = (mu mg)/( cos 60^(@) - mu sin 60^(@))`
`((1)/(2sqrt3) xx sqrt3 xx 10)/((1)/(2)- (1)/(2 sqrt3) xx (sqrt3)/(2) ) = (5)/((1)/(4)) = 20 N`