00:02
Hello, this question requires the application of the laws of newton, the first law specifically, for a body in equilibrium.
00:16
We have a mass ma but exerts a weight of mag, 30 to another mass of mass mb, and of course the weight here is mbg.
00:37
There is friction acting and the coefficients of static and kinetic friction are given a 0 .4 and 0 .2 respectively.
00:54
In the first part we are asked to find a minimum mass ma that will keep this body from sliding.
01:03
So the body does not move in the first place and we are talking about static friction holding it at post.
01:10
And so for such an equilibrium, we expect that the static frictional force opposing the motion must be equal to the weight that intends to move the body.
01:24
There should be that balance between the weight trying to move the body down and the static friction trying to prevent that.
01:35
Now the static frictional force is given by the coefficient of static friction times r.
01:42
But we can tell from the equilibrium in a vertical direction that our r is simply mag.
01:55
Therefore, for equilibrium, mu m -m -a -g, which is the static fractional force, must be equal to mbg.
02:13
Making ma the subject meets to mb over 0 .4 or 2 .5 md...