Answer:
the time taken for the motor to lift the object is 21.17 s.
Explanation:
Given;
mass of the object, m = 45 kg
height through which the object was lifted, h = 9.0 m
electrical power used by the motor, P = 750 W
Efficiency of the electrical motor, n = 25% = 0.25
The electrical energy used by the motor in lifting the object is calculated as;
E = P x t
where;
t is the time taken for the motor to lift the object
E = 750 x t
E = 750t
The electrical energy converted by the motor to mechanical energy is calculated as;
P.E = 0.25(750t)
P.E = 187.5t
Recall, P.E = mgh
mgh = 187.5t
45 x 9.8 x 9 = 187.5t
3969 = 187.5t
t = 3969/187.5
t = 21.17 s
Therefore, the time taken for the motor to lift the object is 21.17 s.
