Answer
(c)
Work Step by Step
First, convert 4 MJ to watt-hours: 4 MJ = 4,000,000 watt-hours. Then, divide the total watt-hours by the wattage of each bulb: 4,000,000 watt-hours / 50 watts = 80,000 bulbs. Since each bulb is on for 1 hour, you can run 80,000 bulbs / 1 bulb per hour = 80,000 bulbs per hour. If you run the bulbs for 1 hour each, you can run 80,000 bulbs. However, if you run each bulb for an average of 1 hour per day, you can run 80,000 bulbs / 24 hours = 3333.33 bulbs per day (approximately).
First let's convert the battery's energy available per day to joules:
$4\text{ MJ} = 4000000\text{ joules}.$
The energy used by one $50$ W bulb for $1$ hour is:
$\text{Power}\times\text{Time} = 50\text{ watts} \times 3600\text{ seconds} = 180000\text{ joules}.$
Now divide the total energy by the energy per bulb:
$\frac{4000000\text{ J}}{180000\text{ J/bulb}}\approx
22.22$
So, we can run approximately $22$ bulbs for $1$ hour each.
The answer is (c).
