1. The problem statement, all variables and given/known data A box of mass M is at rest on a horizontal table. The coefficient of static friction between the box and the table is k. The box is connected by a taut string to a block of unknown mass m, initially held horizontally as shown and then released. The box begins to slide at the instant the block reaches the bottom point of its swing. (See attached figure.) Find the mass m of the block. 2. Relevant equations Ff=kN G=mg (g=9.8) most likely work and energy equations such as K=kinetic energy=1/2mv2, Ug=potential energy due to gravity=mgh, W=work=∫Fdr, U=prtential energy=-∫Fdr, etc. 3. The attempt at a solution I need help understanding where I went wrong and how to complete this problem using work and energy considerations. Ff=kN N=-GM and GM=Mg so Ff=kMg The block begins to move when the force of friction is overcome so T=tension in string=kMg. This is where I start getting lost. I did T=Gm=mg so kMg=mg and m=kM.