## Engineering Mechanics: Statics & Dynamics (14th Edition)

$t=30.5s$
The required time can be determined as follows: The work done by the man is given as $U=Wh$ $\implies U=150(15)=2250lb\cdot ft$ The power generated by the man is $P_m=\frac{U}{t}$ $\implies P_m=\frac{2250}{4}=562.5\times \frac{1}{550}=1.02hp$ Now, the power of the bulb is given as $P_b=100\times (\frac{550bl\cdot ft/s}{746W})=73.73lb\cdot ft/s$ We know that $t=\frac{U}{P_b}$ We plug in the known values to obtain: $t=\frac{2250}{73.73}$ $\implies t=30.5s$