Wednesday
October 1, 2014

Homework Help: Science

Posted by Carly on Tuesday, May 15, 2012 at 7:09pm.

1. An electric space heater draws 15.0 A from a 120 V source. It is operated, on average, for 5.0h (hours) each day. a) How much power does the heater use and b) At $.10 per kWh, what does it cost to operate the heater for 30 days?
2. Suppose each person in the United States uses 12,000 kWh of electricity a year and the power plants using coal to generate electricity are 40% efficient. If 1.0 kg of burned coal releases 33.0 mJ a) how much coal will be burned during a year for a family of four b) how large a pile of coal would that be (using 2620 kg/ m^3) c) how much heat is given off to the environment
3. A light bulb uses 65 watts (used for 6 hours a day) and a digital clock uses 5 watts (used for 24hrs a day). Find the cost of operating each one for 30 days. Assume the price is $.10 per kWh

The equations given=
power= current x voltage, energy= power x time, cost= energy x price



I can find a) at 1800 w (watts), but I have no idea where to start on part b.
For 2, I'm unsure of where to star. I know the family of four would use 48,000 kWh a year, but after that, I'm lost. Could you please help explain it to me?

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