there is a block steel placed on a table,and a hanging steel ball is connected to the block by a string.?

Answer 1

I'm assuming there is a friction (coefficient u) between the block and the table and no friction on the string. The block will move when:

W(ball)=uW(block) where:

W(ball)- weight of the ball
W(block) - weight of the block
u - coefficient of friction

Answer 2

So what's the question?

I assume the ball hanges from a pulley and the other end of the string is on the block on a horizontal table. OK.

At the verge of slippage:
Gravity on the ball = mball g
= max friction on the block = mblock * g * mu

Solve for whatever you want.
mball = mblock * mu

Answer 3

False.