- Homework Statement:
- Newton's second law on a compound pendulum
- Relevant Equations:
- I*α = ΣM, F=-kx, G=mg
I need to write an equation for Newton's second law for the above system, where k1=k2 (both springs are the same). The red line represents a bar with m=2kg, l=2m.
I know that I*α = M1 + M2 + M3
If we displace the bar by x, we get the angle of displacement theta.
I know that, judging by the picture, tan(Θ)=x/l, thus x=tan(Θ)*l.
However, my workbook states that M1=-k*tan(Θ)*l*l*cos(Θ). Where did the l*cos(Θ) come from?