A 4.0 kg block is stacked on top of a 12.0 kg block, whcih is accelerating along a horizontal table at a = 5.2 s^-2 m. Let Mu k = Mu s = Mu.

Question

(a) What mininum coefficent of friction Mu between the two blocks will prevent the 4.0 kg block from sliding off?

(b) If Mu is only half this mininium vale, what is the acceleration of the 4.0 kg block with respect to the table, and

(c) with respect to the 12.0 kg block?

(d) What is the force that msut be applied to the 12.0 kg block in (a) and in (b), assuming that the table is frictionless?

ok...

what does it mean by "and in" in the last paragraph...

for now I just need help in part (a) ok on the top free body diagram...

force to the left of static friction

force to the right is the force... the force that the 12.0 kg block is experiancing to move 5.2 s^2 m ????

I would find that force by applying newtons second law which I know how to do but do I include friction on the bottom block???? Couldn't really tell from the way the problem was worded

ok once I know the force that the bottom block has applied to it to find the force of the block resting on top... the force that is opposing the force of firction... how do I find that is it the same as the one the bottom one experiances... Isn't the top block experiancing no opposing force to the force of friction because it's not moving? So how do I find the mininum...

I need help on part (a)

Answer 1

i don't see how to apply Newtons second law to the top block

there's a force pointing left the force of static friction

is there a force opposing this force pointin in the right direction?

How do I find the mininum coefficent of friction

Answer 2

Friction is moving the top block. IT has to equal ma.

friction is 4g*mu
so 4*9.8*mu=4*5m/s^2 solve for mu. That is the min mu to keep the block from sliding off.

Answer 3

Isn't
net force x direction = -Ffr sense it's in the left direction then I would get a negative Mu???

Answer 4

Were did 4.5 s^-2 m come from???

Answer 5

wouldn't it have a zero acceleration sense it's suppose to not be moving

Answer 6

ma=4kg*5.2m/s^2

I don't know your left/right sign conventions. However I do know if the top block is accelerating, the accelerating force must be in the direction of the motion. The bottom block is accelerating. Friction is the force that is moving the top block.

Answer 7

hmmmmmm interesting

THANKS YOU

Answer 8

also is the talbe frictionless or not I couldn't understand by the way it was worded