Question

18.1
A body does 20 J of work in 5 seconds. Calculate its power in watts.
18.2 An electric bulb consumes 7.2 kJ of electrical energy in 2 minutes. Calculate the power of the bulb.
18.3 What is the power of a pump which takes 10 seconds to lift 100 kg of water to a water tank situated
at a height of 20 m? (Consider g = 10 m/s2)
18.4 Four bulbs, with the power of 10 W each, are lit for 30 minutes. Calculate the electrical energy
consumed by them.​

Answer 1

Answer:

18.1 4 watts

18.2 60 watts

18.3 2000 watts

Explanation:

18.1 power = work/time

                 =20J/5s

                =4 watts

18.2 power = work/time

                  =Joules/seconds

                  =1000 J = 1 kJ

                  =7.2 kJ * 1000

                  =7200 J

                  = 60 seconds = 1 minute

                  =60 * 2

                  =120 seconds

                  = work/time= 7200/120

                  =60

18.3 work = mgh

        m = 100 kg

        g = 10m/s2

        h = 20 m

           = 100 x 10 x 20 = 20 000J

       power = work/time

                  = 20 000/10

                  = 2000 watts

Answer 2

Explanation:

18.1 A body does 20 J of work in 5 seconds. Calculate its power in watts.

18.2 An electric bulb consumes 7.2 kJ of electrical energy in 2 minutes. Calculate the power of the bulb.

18.3 What is the power of a pump which takes 10 seconds to lift 100 kg of water to a water tank situated

at a height of 20 m? (Consider g = 10 m/s2)

18.4 Four bulbs, with the power of 10 W each, are lit for 30 minutes. Calculate the electrical energy

consumed by them.