Question

★review exercises 5.7
find the kilowatt hours.

1. current: 2 kw

time: 4 hr.
kwhr:

1. current: 4 kw

time: 15 min.
kwhr:

1. current: 900 watts

time: 24 hr.
kwhr:

1. current: 1,200 watts

time: 30 min.
kwhr:

1. current: 1,500 watts

time: 10 hr.
kwhr:

1. current: 100 watts

time: 34 hr.
kwhr:

Explanation:

Step1: Convert units if necessary

For problems where power is in watts, convert to kilowatts by dividing by 1000. For time in minutes, convert to hours by dividing by 60.

Step2: Use the formula \( \text{Kwhr}=\text{Power (kw)}\times\text{Time (hr)} \)

1. \( \text{Kwhr}=2\times4 = 8 \)
2. Convert 15 minutes to hours: \( 15\div60 = 0.25 \) hr. Then \( \text{Kwhr}=4\times0.25 = 1 \)
3. Convert 900 watts to kw: \( 900\div1000 = 0.9 \) kw. Then \( \text{Kwhr}=0.9\times24 = 21.6 \)
4. Convert 1200 watts to kw: \( 1200\div1000 = 1.2 \) kw. Convert 30 minutes to hours: \( 30\div60 = 0.5 \) hr. Then \( \text{Kwhr}=1.2\times0.5 = 0.6 \)
5. Convert 1500 watts to kw: \( 1500\div1000 = 1.5 \) kw. Then \( \text{Kwhr}=1.5\times10 = 15 \)
6. Convert 100 watts to kw: \( 100\div1000 = 0.1 \) kw. Then \( \text{Kwhr}=0.1\times34 = 3.4 \)

Answer:

1. \( 8 \)
2. \( 1 \)
3. \( 21.6 \)
4. \( 0.6 \)
5. \( 15 \)
6. \( 3.4 \)