# Conservation of energy with a mass and pulley system.

by sdoi
Tags: conservation, energy, pulley, tension, velocity
 P: 37 1. The problem statement, all variables and given/known data Two boxes are attached to opposite ends of a rope passing over a frictionless pulley as shown below. The mass of Box A is 15kg and the mass of box B is 12kg. The system is originally at rest with the bottom of box A at a height of o.85m above the floor. When the system is released, the boxes will move. Use conservation of energy to determine the speed with which Box A will contact the floor. 2. Relevant equations Eg=mgΔh Ek= 1/2 mv^2/2 ƩFy=may 3. The attempt at a solution I started off by drawing free body diagrams of each mass, one at rest, and one in motion. For mass A: at rest, ƩFy=0 Ft+Eg=0 Ft= Eg = mgΔh =(15kg)(9.8m/s^2)(0.85m) Ft=125N in motion, ƩFy= may Fg(A)-Ft= m(A)ay For mass B: at rest, ƩFy=0 Fn-mg=0 Fn=mg =(12kg)(9.8m/s^2) Fn=117.6N in motion, ƩFy=may Ft-Fg(B)= m(B)ay I'm not sure if my original statement of Ft=Eg is accurate... and from this point on I don't know where to go.
 P: 910 Why not find the initial and final energies and equate them?
 P: 37 As in, Etotal= Eg, Etotal'=Ek ?
P: 910

## Conservation of energy with a mass and pulley system.

System is originally at rest. Hence initial energy = ...
Final energy = ...

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