Question 2.1: An elevator must lift a load of 4000 lb to a height of 50 ft......

Find the amount of work that must be performed, and then convert that to horsepower:

4000 lb \times 50 ft = 200,000 ft-lb

\frac{200,000\ \;{\mathrm{ft-lb}}}{20\,{\mathrm{s}}} = 10,000 ft-lb/s

\frac{10,000\ ft-lb/s}{550\ ft-lb/s} = 18.18 hp