Answer:
the force must be equal to 8.888 N to keep it from slipping
Step-by-step explanation:
We have given weight of the bulletin board W = mg =4 N
Coefficient of static friction
![\mu =0.450](https://img.qammunity.org/2020/formulas/physics/middle-school/76gj5j31ve8ca0cr9qxzm6os98idiuwmz6.png)
When frictional force balance the weight
Then
![\mu N=mg](https://img.qammunity.org/2020/formulas/physics/middle-school/stcloyf364oaac66tbcy95k00b8ukclo4l.png)
So
![0.450* N=4](https://img.qammunity.org/2020/formulas/physics/middle-school/1z4nb4zpphfc9iakt9oimblqibb5hguxqq.png)
![N=(4)/(0.450)=8.888N](https://img.qammunity.org/2020/formulas/physics/middle-school/cafjoik3sj8z518bk6cmfszjjh8llqr24m.png)
So the force must be equal to 8.888 N to keep it from slipping