a machine lifts a 50 kg mass to a height of 60 m in 4s. Calculate the power developed by the machine (take g= 10 m/s)​​

Explanation:

Power is given by , where is work and is elapsed time. To calculated work, we'll use , where is force and is displacement. Substituting given values, we have:

.

Now plugging this in to our power equation, we get:

The power developed by the machine is 7700 Watt.

Explanation:

what is the speed of a softball that travels 20m in 2secs

speed = 20/2 = 10 m/s

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.