OATBooks.com Forum for Discussion https://www.oatbooks.com/forum/ 

Re: Practice Test Physics # 4 https://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 kilowatthour (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 $1 B. Between $1 and $5 C. Between $5 and $50 D. More than $50 E. 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 “kilowatthour (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 Group
http://www.phpbb.com/ 