Chapter 7, Problem 74MSPP

The Bunchberry

The bunchberry flower has the fastest-moving parts ever seen in a plant. Initially, the stamens are held by the petals in a bent position, storing energy like a coiled spring. As the petals release, the tips of the stamens fly up and quickly release a burst of pollen.

Figure P7. 72 shows the details of the motion. The tips of the stamens act like a catapult, flipping through a 60° angle; the times on the earlier photos show that this happens in just 0.30 ms. We can model a stamen tip as a 1.0-mm-Jong, 10 μg rigid rod with a 10 μg anther sac at one end and a pivot point at the opposite end. Though an oversimplification, we will model the motion by assuming the angular acceleration is constant throughout the motion. P7.751Q

Figure P7.72

74. How large is the “straightening torque”? (You can omit gravitational forces from your calculation; the gravitational torque is much Jess than this.)

A. 2.3 × 10^–7 N · m

B. 3.1 × 10^–7 N · m

C. 2.3 × 10^–5 N · m

D. 3.1 × 10^–5 N · m