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# Physics costing electricity, KW/KWh

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Mitzi on 4 Dec 2022
Closed: Jan on 4 Dec 2022
This question was flagged by Dyuman Joshi
How long could you run a 2 kW hairdryer on 50p if electricity costs 7.5p per unit?
##### 1 CommentShowHide None
Image Analyst on 4 Dec 2022
This looks like a homework problem. If you have any questions ask your instructor or read the link below to get started:
Obviously we can't give you the full solution because you're not allowed to turn in our code as your own.

### Answers (1)

VBBV on 4 Dec 2022
Edited: VBBV on 4 Dec 2022
% assume
P_rating = 2e3; % 2000 W = 2kW
number_units = 50/7.5 % since each unit is treated as 1kWh @ 7.5p per unit
number_units = 6.6667
run_time = number_units /(P_rating/1000) % apprx run time in hours
run_time = 3.3333
##### 1 CommentShowHide None
VBBV on 4 Dec 2022
The above is true if you consider the device to operate at its rated power otherwise, there will be more possibilites.
% assume
P_rating = [1e3 2e3]; % 2000 W = 2kW is nominal rating of device , 1e3 is power when device can work at lower speeds
number_units = 50/7.5 % since each unit is treated as 1kWh @ 7.5p per unit
number_units = 6.6667
run_time = number_units ./(P_rating/1000) % apprx run time in hours
run_time = 1×2
6.6667 3.3333

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