ANSWER:
1st option: 6.3 min
STEP-BY-STEP EXPLANATION:
Given:
Work (W) = 4.5x10^5 J
Mass (m) = 1000 kg
Height (h) = 0.8 m
Time (t) = 6 h
1 hour is equal 3600 sec, therefore:
[tex]6\text{ h}\cdot\frac{3600\text{ sec}}{1\text{ h}}=21600\text{ sec}[/tex]
Time (t) =21600 sec
We have the following formula (Power):
[tex]P=\frac{W}{t}^{}[/tex]
We replace the values of this case:
[tex]\begin{gathered} P=\frac{4.5\cdot10^5}{21600} \\ P\: =20.83\text{ W} \end{gathered}[/tex]
Now we calculate the work in the form of potential energy needed to lift the bricks:
[tex]\begin{gathered} W=m\cdot g\cdot h \\ \text{ we replacing} \\ W=1000\cdot9.8\cdot0.8 \\ W=7840\text{ J} \end{gathered}[/tex]
Now, we can calculate the time by calculating the ratio between the work and the power, like this:
[tex]\begin{gathered} P=\frac{W}{t} \\ t=\frac{W}{P} \\ \text{ we replacing} \\ W=\frac{7840}{20.83} \\ W=376.4\text{ sec} \end{gathered}[/tex]
This is the time in seconds, to convert it to minutes, we must take into account that 1 minute is equal to 60 seconds, therefore:
[tex]376.4\text{ sec}\cdot\frac{1\text{ min}}{60\text{ sec}}=6.27\cong6.3\text{ min}[/tex]
The time it would take is 6.3 minutes
