Quick Physics Question? (1 Viewer)

[Zokunu]

littlehelp?

If electricty cost 15c per kilowatt-hour calculate i) The energy consumed ii) cost of using:

a) 2000W radiator for 6 hours
b) a 100W globe and a 1kW radiator for 3 hours
c) a 7200W water heater for 15 mins

thanks

 

[HSC2014]

Well the watt is a measurement of joules per second, so from there you should be able to answer the questions. Also, the kilowatt-hour is just a unit of energy consumption used for convenience and manageability (as you will see in the first example)
Here's the first one:
ai. 2000J/s x (6 x 60 x 60)s = 43200 KJ (or 43200000 J)
ii. The appliance is using 2kW for 6 hours - so (2 x 6) x 15c = $1.80 (180 c)

 

[Zokunu]

Well the watt is a measurement of joules per second, so from there you should be able to answer the questions. Also, the kilowatt-hour is just a unit of energy consumption used for convenience and manageability (as you will see in the first example)
Here's the first one:
ai. 2000J/s x (6 x 60 x 60)s = 43200 KJ (or 43200000 J)
ii. The appliance is using 2kW for 6 hours - so (2 x 6) x 15c = $1.80 (180 c)

bump, thanks man, appreciate it . Just wanna ask another question:

A student is using a luxmeter to measure the intensity of light at various distances from a light source. At distance, d, the intensity is measured as 1 units.
If the distance is reduced to d/2 the intensity would be closest to....

(a) 1/2
(b) 1/4
(c) 21
(d) 41

The answer is D....but how?
Thanks

 

[HSC2014]

Options c and d are meant to be 2 and 4 respectively

The intensity of light is inversely proportional to the square of its distance from the source (i.e. Intensity ∝ 1 / d^2 ).
So if 1/d^2 = 1 unit then 1 / (d/2)^2 = 4 (use mathematics here)

 

[Zokunu]

Options c and d are meant to be 2 and 4 respectively

The intensity of light is inversely proportional to the square of its distance from the source (i.e. Intensity ∝ 1 / d^2 ).
So if 1/d^2 = 1 unit then 1 / (d/2)^2 = 4 (use mathematics here)

mhm, thx man, i though that was a 1 at the end ==''. Just want to check somethin

A small car of mass 800kg moves from a stationary position to a speed of 60km/h in 10 seconds.

(a) Calculate the average acceleration of the car. is it.....?

60-0/3.6x10
= 1.67m/s^2?

Do i ignore the 800kg?