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**1. Homework Statement**

this question is about a pendulum's speed. the string is 1.0m long, in which r=1m. it says the tension is twice of the bob's weight when the string is vertical, which means when its at the bottom point of the circular motion.

**2. Homework Equations**

since [tex]F_T[/tex] should overcome [tex]F_g[/tex], so [tex]F_c=F_T-F_g[/tex].

here is how i solve this question:

[tex]F_c=F_T-F_g=\frac{mv^2}{r}[/tex]

[tex]{2F}_g-F_g=\frac{mv^2}{r}[/tex]

[tex]F_g=\frac{mv^2}{r}[/tex]

[tex]g=\frac{v^2}{r}[/tex]

sub in, then v should be equal to about 3.13m/s

**3. The Attempt at a Solution**

i got this answer twice, but the teacher said im wrong.