Power (plenary exercises)

What is meant by power?

The unit of power is the

(a)  

Which of the following is the correct formula/e to calculate power?

• power = energy X time

• power = energy/time

• power = workdone/time

• power = workdone x time

An airplane engine does 1000J of work in 10s. What is the power of the engine?

• 10 W

• 100 W

• 1000 W

• 10000 W

A boy walks up the stairs using 150J of energy in 30s. What is the boy's power.

• 0.2 W

• 5 W

• 45 W

• 450 W

Another boy walks up the same stairs with the same amount of energy of 150J but taking only 20s. Calculate what is (i) the boy's power and (ii) is he more powerful or less powerful than the previous boy? Why

An electric motor can lift a weight of 2000 N through a vertical height of 10 m in 20 s. What is the power of the motor.

• A 10 W

• B 1000 W

• C 4000 W
  

• D 400 000 W

A small motor has a power rating of 10 W and is run for 5 min. How much electrical energy does it convert in this time?

• A 2J

• B 50J

• C 60J

• D 300 J

• E 3000 J