Question

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

a. `100N`
b. `80N`
c. `50N`
d. `20N`

Answer 1

`c. 50N`

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=mg=20`

and,frictional force acting is `mu N=muF=0.40F` (as, `F=N`)

So,we can equate to write,

`0.40F=20`

or, `F=50N`

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