# Physics

I only need help with part B.

A 250W computer power
supply is on 10 h per day.

Part A
If the cost of electricity is \$0.15/kWh, what is the energy cost (to the nearest dollar) if this computer is used like this for a year (365 days)?
140 dollars

Part B
If this power supply is replaced by a more efficient 100-W version and it costs \$100, how long will it take the decreased operating cost to pay for this power supply? (in years)

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3. 👁 100
1. A. 0.250kW * 10h/day * 365days/yr. =
912.5 kWh./yr

Cost = 912.5kWh/yr * \$0.15/kWh=\$137/yr.

B. (0.100/0.250) * 912.5kWh/yr=365kWh/yr

Cost = 365kWh/yr * \$0.15/kWh = \$55/yr

Savings = 137 - 55 = \$82/yr

\$100/\$82 = 1.22 Years.

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2. 👎 0
posted by Henry

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