Apulley stems has an efficiency of 65.1%. if you perform 350 j of work, how much useful work does the pulley perform?

a. 350 j
b. 301 j
c. 228 j
d. 122 j

C. 228 Joules

Efficiency of a machine is the energy or work output, divided by the energy or work input, and expressed as a percentage. An ideal machine would have an efficiency of 100%.

Efficiency = (work output/work input) × 100%

work input = 350 joules, efficiency = 65.1%

Work output = 350 j × 65.1/100

                    = 227.85

                    ≈ 228 Joules

what is the actual question though?

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.