PHYSICS · Multi-part · CBSE · Physics · Work, Energy and Power · Work, Energy and Power
Problem
A bucket of mass 4.0kg is attached to a light, inextensible string that passes over a frictionless, massless pulley. The other end of the string is tied to a 1.0kg block that rests on a horizontal, frictionless table. Initially both objects are at rest, and the bucket is 1.2m below the level of the tabletop. When the bucket is released, it falls vertically while pulling the block across the table.
Ignore air resistance and assume the string does not slip on the pulley.
(a) Define a system boundary for which mechanical energy is conserved as the bucket falls. Clearly state which objects are included and which are excluded, and briefly justify your choice.
(b) Using the system you defined in part (a), determine the speed of the bucket after it has descended 1.2m.
(c) Suppose instead that the system had been defined as the bucket alone. Calculate the magnitude of the work done on the bucket by forces external to this system during the 1.2m descent.
(d) State whether the work you found in part (c) is positive, negative, or zero, and explain what physical feature of the situation leads to that sign.