Question

You need to purchase a motor to supply 400 joules in 20 seconds all of the motors you can choose from are 70% efficient. what is the minimum wattage on motor you need to purchase

Answer 1

Power = Energy / Time
= 400 J / (20 s)
= 20 Watt

A 100% efficient motor will provide 20 Watt power. But all the motors are 70% efficient. So the minimum wattage on motor should be
70% of x = 20 Watt
x = 20 Watt / (70 %)
x = 28.57 Watt