1. The problem statement, all variables and given/known data I don't really understand how to approach problems like these A lift has a downward acceleration of kg (k<1). Inside the lift is mounted a pulley, of negligible friction and inertia, over which passes an inextensible string carrying two objects of masses m and 3m. a. Let the Tension in the string be T and the accelerations of the 3m and m masses be a1 and a3. Write down the equations of motion of the two masses in terms of T. b. Eliminate T, relating a1 and a3 c. Use the information that the string is inextensible to get another relationship between a1 and a3 (one way to use this information is to set up equations relating the motion in the inerital (shaft) frame to the non-inertial (lift) frame) d. For k=1/3 find the acceleration of the 3m mass in the lift frame and the force exerted on the pulley by the rod that joins it to the roof of the lift. 2. Relevant equations 3. The attempt at a solution a. 3mg - T = 3ma3 and mg - T = ma1 b. 2g = 3a3 - a1 c. In the lift frames, the accelerations are a1' and a3' a1' = a1 - kg and a3' = a3-kg But a1'=-a3' (as the string is inextensible) Inserting a1'=-a3' and equating above equations: a1-kg = kg = a3 I put this back into the equation of part (b) to get a3 in terms of k, but it was wrong. I'm sure I'm doing something fundamentally wrong, so please help! The answers given are g/3 for the acceleration of 3m in the lift frame and 2mg for the force on the pulley.