OATBooks.com Forum for Discussion https://www.oatbooks.com/forum/ Re: Practice Test Physics # 4https://www.oatbooks.com/forum/viewtopic.php?f=17&t=90 Page 1 of 1
 Author: amishley1421 [ Wed May 29, 2019 2:46 pm ] Post subject: Re: Practice Test Physics # 4 4. Given a cost of electricity of \$0.15 per kilowatt-hour (kWh), how much is saved by switching from a 60 watt light bulb to a 25 watt compact fluorescent bulb for 200 hours? A. Less than \$1B. Between \$1 and \$5C. Between \$5 and \$50D. More than \$50E. Explanation:This is strictly a problem of dimensional analysis (i.e. paying attention to the units to get a mathematical result). Begin by identifying a kilowatt as a thousand watts and a “kilowatt-hour (kWh)” as a kilowatt multiplied by an hour. The power saved would be 60 – 25 = 35 watts Convert watts to kilowatts: 35 watts x (1 kW/1000 watts) = 0.035 kW Multiply kW by hours: 0.035 kW x 200 h = 7.0 kWh Multiply kWh by cost/kWh: 7.0 kWh x \$0.15/kWh = \$0.85 which is less than \$1.-----------------------------------------------------------------------------------------------------------------------7*0.15 = 1.05 So isn't the answer B
 Author: mnlarson4143 [ Wed Nov 06, 2019 9:28 am ] Post subject: Re: Practice Test Physics # 4 Did the same thing. I think it's B.
 Page 1 of 1 All times are UTC - 6 hours Powered by phpBB® Forum Software © phpBB Grouphttp://www.phpbb.com/