Power questions

f) Power is the rate of doing work.

Power (in Watt) = Work done (in Joules) / time (in seconds)

g) 1 watt is a rate of working of one Joule per second.

13) A girl does 1000 joules of work in 5 seconds. What power does she develop?

P = E / t = 1000J / 5s = 200 Watts

14) A man lifts a weight of 300N through a vertical height of 2m in 6 seconds. What power does he develop?

Wd = F x d

Wd = 300 x 2

Wd = 600 Joules

P = E/t

P = 600 / 6 s

P = 100 Watts

16) A crane lifts a load of 3000N through a vertical height of 10 m in 4 seconds. What is its rate of working in a) Watts b) Kilowatts?

Wd = F x d0

Wd = 3000 x 10

Wd = 30000 Joules

P = E/t

P = 30000J / 4s

P = 7500 Watts

OR

7.5 Kilowatts