A 4.5 kW electric motor is 90% efficient. How much energy does it use in 20 seconds?
- 4.5 kJ.
- 810 kJ.
- 100 kJ.
Explanation from PART66Online
The motor's useful output over 20 s is 4.5 kW x 20 s = 90 kJ. Because it is only 90 per cent efficient, the electrical energy it draws is 90 / 0.9 = 100 kJ, the extra being lost as heat. Input energy is always greater than useful output.
R
rizkaramat asked · 15 Apr 2012
can somebody plz solve
Community Comments (6)
C
chris146
25 Apr 2012
using E=ITV and P=IV. combine to make E= T x P.
E=20 x 4500 = 90kJ. Answer is wrong I think...
E=20 x 4500 = 90kJ. Answer is wrong I think...
C
chris146
25 Apr 2012
and its 90% efficient... so 90000 = 90%. 100% = 100000J
C
chris146
25 Apr 2012
so its not wrong!
A
alberto
7 Apr 2013
when calculating energy always take 100% as the efficiency then you can solve the problem by using the equation ENERGY = POWER * TIME.
3
3g_nitro
10 May 2015
Similar to what Chris said but different way of solving:
If 4.5 kW = 90 % then (using ratios)
5 kW = 100%
Then using P = W/T => W=PxT
W = 5000 X 20 = 100kJ
:)
If 4.5 kW = 90 % then (using ratios)
5 kW = 100%
Then using P = W/T => W=PxT
W = 5000 X 20 = 100kJ
:)
D
Diverdeep
11 Apr 2023
should be written in another way, in this way, I understand 4.5 is the nominal power of the motor, not the effective work (output)
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