An elephant\'s legs have a reasonably uniform cross section from top to bottom,

Question

An elephant's legs have a reasonably uniform cross section from top to bottom, and they are quite long, pivoting high on the animal's body. When an elephant moves at a walk, it uses very little energy to bring its legs forward, simply allowing them to swing like pendulums. For fluid walking motion, this time should be half the time for a complete stride; as soon as the right leg finishes swinging forward, the elephant plants the right foot and begins swinging the left leg forward. An elephant has legs that stretch 2.3m from its shoulders to the ground. How much time is required for one leg to swing forward after completing a stride? I have tried 3.04secs, 1.52 secs, 1.76 secs, and 0.88 secs and none of them are correct.  If you can walk through the problem step by step I just don't undertstand why those answers are not correct. An elephant's legs have a reasonably uniform cross section from top to bottom, and they are quite long, pivoting high on the animal's body. When an elephant moves at a walk, it uses very little energy to bring its legs forward, simply allowing them to swing like pendulums. For fluid walking motion, this time should be half the time for a complete stride; as soon as the right leg finishes swinging forward, the elephant plants the right foot and begins swinging the left leg forward. An elephant has legs that stretch 2.3m from its shoulders to the ground. How much time is required for one leg to swing forward after completing a stride? I have tried 3.04secs, 1.52 secs, 1.76 secs, and 0.88 secs and none of them are correct.  If you can walk through the problem step by step I just don't undertstand why those answers are not correct.

Explanation / Answer

T = 2pi*sqrt(I/mgd)

Here

I = Moment about one end of the rod like leg

= (1/3)mL^2

= 2.3^2/3 *m

= 1.7633m

d = L/2 = Distance between COM and Point of contac

= 0.5*2.3

= 1.15 meter

Therefore

T = 2pi*sqrt(1.7633/(9.8*1.15))

= 2.485 se

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