Question

a) Which of the following does not represent unit of energy?
a. Nm b. J c.W/s d.kgm2s-2
b) In a staircase running race, John of weight 600 N takes 1 minute 20 seconds to run up a 20-storey building. The height of each storey is 3 m. Estimate the average power developed by John. Take g = 10 m /s/s.

Answer 1

a) W/s

it is not the unit of energy cause it is the unit of power

all the other units are units of energy as well as work

work = energy

b) Power = W/t

W = F s

W = mgh

F = ma

a = g

m = F/a

= 60 x 10 x 20 x 3

1 min 20 sec = 80 sec

P = 60 x 10 x 20x 3 / 80

= 36000/80

= 450W

hope it helps...