Question

a windmill captures 700w of wind power for 10h. the kinetic energy is converted to electric energy and stored in a battery, before being used by a 60w light bulb. during the process 65% of the energy is lost. wind energy captured w h loss. w h energy delivered to light bulb: w h how long could the light bulb be used? hours

Explanation:

Step1: Calculate wind - energy captured

The power of the windmill is $P = 700W$ and the time is $t = 10h$. Using the formula $E=P\times t$, the wind - energy captured $E_{captured}=700\times10 = 7000Wh$.

Step2: Calculate energy loss

The energy loss is 65% of the captured energy. So, $E_{loss}=0.65\times7000 = 4550Wh$.

Step3: Calculate energy delivered to the light - bulb

The energy delivered to the light - bulb $E_{delivered}=(1 - 0.65)\times7000=0.35\times7000 = 2450Wh$.

Step4: Calculate the time the light - bulb can be used

The power of the light - bulb is $P_{bulb}=60W$. Using the formula $t=\frac{E}{P}$, the time $t=\frac{2450}{60}=\frac{245}{6}\approx40.83h$.

Answer:

wind energy captured: 7000 Wh
loss: 4550 Wh
energy delivered to light bulb: 2450 Wh
How long could the light bulb be used: $\frac{245}{6}\approx40.83$ hours