Question

(a) State and define SI unit of power. 

(b) A person carrying 10 bricks each of mass 2.5 kg on his head moves to a height 20 m in the 50s. Calculate power spent in carrying bricks by the person (g = 10 m/s²)

Answer 1

(a) The rate of doing work is called as the power. The SI unit of power is Watt denoted by W. 

1 Watt is the power of appliances that consume the energy at the rate of 1 joule per second

(b) Given 

Mass of brick = 2.5 kg 

⇒ Weight = mg = 2.5×10 = 25 N 

Weight of 10 bricks = 25×10 = 250 N 

Height (h) = 20 m 

Time (t) = 50 s

Power = \(\frac{Work\,done}{Time\,taken}\)

⇒ Power = \(\frac{mgh}{t}\) = \(\frac{250\times20}{50}\)

= \(\frac{5000}{50}\) = 100 W

Power spent in carrying bricks is 100 Watt.