The 0.75-kg bob of a pendulum is fired from rest at position a. if the spring is compressed 50 mm and released, determine (a) its stiffness k so that the speed of the bob is zero when it reaches point b, (b) the stiffness k so that when the bob reaches point c the tension in the cord is zero

a coal burning power plant

f=ma newton

f=100x2.5=250n

-4 on

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.