Question

I have a question on the forces on the x axis and if it has friction. so when its acceleration down the incline its Fk-mgsin = -ma? and up its -mgsin - fk = ma? when you explain please draw a picture

Answer 1

Figure (A)

Figure(B)

We know that friction always oppose the tendency of motion.

In figure (A) block move downward so friction is acting in upward direction.

Let in figure(A) block move with downward acceleration 'a' due to gravity then the equation of motion is given as

So,

Now,

Let in figure(B) block moving in upward direction with acceleration 'a' then both gravity and friction will oppose the motion of block and there is no force acting upward direction (let it is 0 N)

Therefore equation of motion is given as :

In this case we can say 'a' is negative means here the block is retarding.