Question

A MAN OF MASS 50KG ASSEND A FLIGHT OF STAIRS 5M HIGH IN 5SECOND IF ACCELERATION DUE TO GRAVITY IS10M PERSECONDSQUARE CALCULATE FOR THE POWER EXPENDED

Answer 1

You have chosen the distance to be about the distance which the light would move in 1 second. I cannot imagine the reflectance of the sphere would be greater than 99%, so if you solve the equation 0.99N=0.001, N would be the number of seconds it would take for the intensity of the light to drop to 0.1% of its original value. Using Wolfram Alpha, I find N≈687, a little more than 11 minutes.

Answer 2

see your previous post.

Answer 3

P = F*d/t = (M*g)*d/t = (500)*5/5 = 500 J./s = 500 Watts.