Question

A motor is used to lift a load of 40 N.

 The power of the motor is 40 W and the system is 20% efficient. How long does it take the motor to lift the load through 0.50 m?

A. 0.50 s

B. 2.5s

C. 5.0s

D. 25s

Answer 1

$$\eta Pt=Fs\\0.2(40)t=40(0.5)\\t=2.5\ s$$

Answer: B. 2.5s