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
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.
rizkaramat asking:
can somebody plz solve
Community Comments (6)
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chris146 Posts: 7 25.04.2012 / 13:33
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...
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chris146 Posts: 7 25.04.2012 / 13:34
and its 90% efficient... so 90000 = 90%. 100% = 100000J
C
chris146 Posts: 7 25.04.2012 / 13:34
so its not wrong!
A
alberto Posts: 8 07.04.2013 / 13:31
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 Posts: 3 10.05.2015 / 18:21
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 Posts: 8 11.04.2023 / 20:24
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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