With the help of a movable block having an efficiency of 50%, a load weighing 40 kg

With the help of a movable block having an efficiency of 50%, a load weighing 40 kg was lifted to a height of 8 m. Determine the force applied to the end of the rope.

These tasks: η (efficiency of the moving unit) = 50% (0.5); m (mass of the lifted load) = 40 kg; h (lifting height) = 8 m.

Constants: g (acceleration due to gravity) ≈ 10 m / s2.

The force that should have been applied to the free end of the rope can be expressed from the formula (we take into account that the movable block will give a gain in strength by 2 times, but does not give a gain in the work expended): η = Ap / Az = ΔEn / (F * S ) = m * g * h = (2F1 * h) = m * g / 2F1, whence F1 = m * g / 2η.

Calculation: F1 = 40 * 10 / (2 * 0.5) = 400 N.