One movable pulley: 8 kg, 2 rope segments

A pulley block with 1 movable pulley lifts an 8 kg load at a steady speed; 2 rope segments support the load, and the load rises 1.2 m. Find the minimum pulling force and the distance the rope end moves. (Take g = 10 N/kg.)

Step-by-step

1. Weight G = mg = 8×10 = 80 N
   Find the weight of the object being lifted first
2. F = G/n = 80/2 = 40 N
   n rope segments share the load, so each needs only G/n (n = 2 ✓)
3. s = n·h = 2×1.2 = 2.4 m
   Less force means more distance: the rope end moves n times the lift height (work is not saved ✓)

Why it works

Two rope segments share the load, so the minimum pull is half the weight, while the rope end must move twice as far as the load rises. The product of force and distance stays the same.

Common mistakes

• Using the 8 kg mass as the force instead of the 80 N weight.
• Thinking the rope end moves 1.2 m as well, not twice that.

Related

pulley-one-movable-minimum-force pulley-two-movable-rope-distance n-phy-pulley-two-1