High School

WJHS uses approximately [tex]$11,000 \text{ kWh}$[/tex] of energy each day to power the building. A kilowatt-hour (kWh) is a unit of energy that is the product of the power developed and the time spent powering the device. In other words, [tex]E = P \cdot t[/tex].

The WJ physics team decides to offer extra credit to students who are willing to provide power to the building by riding an exercise bike. Students ride for 8-hour shifts, and each rider averages 100 W of power for their entire shift.

Calculate how many riders are needed to supply the [tex]$11,000 \text{ kWh}$[/tex] of energy for the school.

Answer :

To solve this problem, let's break it down into steps:

1. Understand the Energy Requirement:
- The building uses 11,000 kilowatt-hours (kWh) of energy each day. We also know this is equal to about [tex]\(4.0 \times 10^{10}\)[/tex] Joules.

2. Energy Provided by Each Rider:
- Each student riding an exercise bike provides an average power of 100 Watts. Remember, 1 Watt (W) is equivalent to 1 Joule per second.
- Each rider works an 8-hour shift. To find out how much energy one rider provides in one shift, we need to convert the time to seconds because power is in Watts (Joules per second).
- There are 3600 seconds in an hour, so in 8 hours, there are [tex]\(8 \times 3600 = 28,800\)[/tex] seconds.

3. Calculate Energy by One Rider:
- The energy provided by one rider in one shift is:
[tex]\[
\text{Energy per rider} = \text{Power} \times \text{Time} = 100 \, \text{W} \times 28,800 \, \text{s} = 2,880,000 \, \text{Joules}
\][/tex]

4. Determine the Number of Riders Needed:
- We need to find out how many riders are required to meet the total energy need of [tex]\(4.0 \times 10^{10}\)[/tex] Joules.
- The number of riders required can be calculated using the formula:
[tex]\[
\text{Number of riders} = \frac{\text{Total energy needed}}{\text{Energy per rider}}
\][/tex]
[tex]\[
= \frac{4.0 \times 10^{10} \, \text{Joules}}{2,880,000 \, \text{Joules per rider}}
\][/tex]

5. Final Calculation:
- Calculating this gives approximately 13,888.89 riders.

So, around 13,889 riders are needed to supply the 11,000 kWh of energy required by the building for one day.