Question

(a) Define power. Give the SI unit of power.

(b) A boy weighing 40 kg carries a box weighing 20 kg to the top of a building 15 m high in 25 seconds. Calculate the power. (g = 10 $m/s^2$)

Answer 1

a)The rate of doing work is called power. Its SI unit is J/sec (Joule/second) or W (Watt).
b)Total mass = 40 + 20 = 60 kg
Work done = $mgh=60\times 10\times 15$
Power = Work done/time
$P=\frac{600\times 15}{25}$
$=\frac{9000}{25}=360W$