Answer:
[tex]t=30.5s[/tex]
Explanation:
Given data
The weight of man W=150 lb
The man can run up stairs of height h=15 ft in time t=4s
The work done by man
[tex]U=Wh\\U=(150)(15)\\U=2250 lb.ft\\[/tex]
The power generated by the man
[tex]P_{man}=\frac{U}{t}\\ P_{man}=\frac{2250}{4}\\ P_{man}=562.5lb.ft/s\\or\\P_{man}=562.5lb.ft/s*(1/550)=1.02hp[/tex]
Power of bulb
[tex]P_{bulb}=100*(\frac{562.5lb.ft/s}{746W} )=73.73lb.ft/s\\t=\frac{U}{P_{bulb}}=\frac{2250}{73.73} \\ t=30.5s[/tex]
