The bunchberry flower has the fastest-moving parts ever observed in a plant. Ini

Question

The bunchberry flower has the fastest-moving parts ever observed in a plant. Initially, the stamens are held by the petals in a bent position, storing elastic energy like a coiled spring. When the petals release, the tips of the stamen act like medieval catapults, flipping through a 60? angle in just 0.29ms to launch pollen from anther sacs at their ends. The human eye just sees a burst of pollen; only high-speed photography reveals the details. As in the following figure shows, we can model the stamen tip as a 1.0-mm-long, 8.0?g rigid rod with a 8.0?g anther sac at the end. Although oversimplifying, we'll assume a constant angular acceleration.(Figure 1)

http://session.masteringphysics.com/problemAsset/1429718/5/K-P12.66.jpg

How large is the "straightening torque"?

Explanation / Answer

alpha = 2 theta / t^2 = 2(60 * 2pi rad/ 360) / 0.29 ms^2

= 2.49 * 10^7 rad/s2

T = I alpha

I = Inod + m r^2

= 1/3 MR^2 + m r^2

= (1/3 * 8 * 10-9 kg (1 * 10-3)^2) + ( 8 * 10-9 kg (1 * 10-3)^2)

= 1.067 * 10-14 kg m2

T = (1.067 * 10-14 kg m2) (2.49 * 10^7 rad/s2)

= 2.66 * 10-7 kg.m

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