Barry walks from one end to the other of a 30-meter long moving walkway at a constant rate in 30 seconds, assisted by the walkway. when he reaches the end, he reverses direction and continues walking with the same speed, but this time it takes him 120 seconds because he is traveling against the direction of the moving walkway. if the walkway were to stop moving, how many seconds would it take barry to walk from one end of the walkway to the other? a) 48b) 60c) 72d) 75e) 80

A. 48 seconds

Explanation:

In one part of the journey the moving walkway helps Barry to arrive faster but does the opposite in the second part of the journey. Let us define B as Barry’s speed and W as the speed of the walkway. We can set two equations as it follows:

B+W = (30 m)/(30 s) =1 m/s

B-W = (30 m)/(120 s) =0,25 m/s

If we add both equations, the speed of the walkway cancels itself and we have:

2*B = 1+0,25 = 1,25 m/s

B = (1,25 m/s)/2 = 0,625 m/s

Knowing Barry’s speed and applying the definition of velocity, we can find the time that it would take him to walk from one end of the walkway to the other without assistance.

v = x/t → t = x/v = (30 m)/(0,625 m/s) = 48 s

Have a nice day! :D

conduction, convection, radiation

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.