# If µ = 0.40 and mg = 20N, what minimum force F will keep the box from falling?

## a. $100 N$ b. $80 N$ c. $50 N$ d. $20 N$

Mar 4, 2018

$c . 50 N$

#### Explanation:

Considering the arrangement to be as follows,

So,here frictional force will be acting upwards so that it can balance the weight of the box,now we need to apply $F$ such that it will help the frictional force just to balance the weight of the box,on applying much force the box will accelerate upwards.

So,we can write, $f = m g = 20$

and,frictional force acting is $\mu N = \mu F = 0.40 F$ (as, $F = N$)

So,we can equate to write,

$0.40 F = 20$

or, $F = 50 N$

So, $c . 50 N$ will be the answer.