## College Physics (4th Edition)

(a) The wings must exert a force of $5.1~N$ (b) The energy stored in the resilin is $0.077~J$
(a) $Y = \frac{F/A}{\Delta L/L}$ $Y$ is Young's modulus $F$ is the force $A$ is the cross-sectional area $\Delta L$ is the change in length $L$ is the original length We can find the required force: $F = \frac{Y~A~\Delta L}{L}$ $F = \frac{(1.7\times 10^6~N/m^2)(1.0\times 10^{-6}~m^2)(3.0\times 10^{-2}~m)}{1.0\times 10^{-2}~m}$ $F = 5.1~N$ The wings must exert a force of $5.1~N$ (b) We can find the energy in the system: $U = \frac{1}{2}~F~\Delta L$ $U = \frac{1}{2}~(5.1~N)(3.0\times 10^{-2}~m)$ $U = 0.077~J$ The energy stored in the resilin is $0.077~J$