A pulley system with VR = 4 is used to lift a load of 175 kgf through a vertical height of 15 m. The effort required is 50 kgf in the downward direction, (g = 10 N kg-1). [4] Calculate:
M.A. of the pulley system.
Topic: Machines, levers and pulleys
Answer
Given: load L = 175 kgf, effort E = 50 kgf
Mechanical advantage = load ÷ effort MA = 175 ÷ 50 = 3.5
Mechanical advantage = 3.5
Mechanical advantage is a pure ratio with no unit, so load and effort simply have to be in the SAME unit — both are in kgf here, so no conversion is needed.
Load on top, effort underneath. Inverting it gives 0.286, and an MA below 1 would mean the machine makes the job harder.
Notice MA (3.5) is less than VR (4). That is always true for a real machine, because some effort is spent against friction and the weight of the moving parts. If your MA ever comes out larger than the VR, something is wrong.