To lift a load weighing 50 kg on an inclined plane 40 cm high, a force of 50 N is required.

To lift a load weighing 50 kg on an inclined plane 40 cm high, a force of 50 N is required. What is the length of this plane if its efficiency is 80%? What is the frictional force when lifting a load?

Given m = 50kg, h = 40cm = 0.4m, F = 50N, efficiency = 80%.
Find l, Ftr.
Efficiency = A useful / A expended = mgh / Fl. From here we find l = mgh / efficiency * F = 5m. To find F friction. We have to build a picture and arrange forces. We arbitrarily designate the angle a. From Newton’s second law. F-Ftr-mgsina = 0 or Ftr = F-mgsina (sina = h / l from the figure). Ftr = F-mgh / l = 10H.