BR physics ch 5 pg 254 number 17

[2010premed]

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In a pendulum, if the initial angle is x, what can be concluded about the angular displacement, y, after half a cycle has eleapsed?

A: y>x

I thought x>y b/c after half a cycle, would the pendulum be at equilibrium?

 

[Rabolisk]

A full cycle returns the pendulum to its original position. A half cycle results in maximum displacement about the equilibrium position. That is, the mass is going from positive amplitude to negative amplitude. The angular displacement y, then is twice the initial angle x. Hence y > x.

 

[2010premed]

Thx! I was starting with it already up

 

[Rabolisk]

I too started with it already up. A full cycle returns you to that position no matter where you start, whereas a half cycle does not, unless you start from equilibrium position..