# Homework Help: T and mg in a pendulum system

1. Sep 26, 2007

### cyclonefb3

I'm having trouble with the idea of tension in a pendulum. I've reasoned out my answers, but they're wrong. Am I missing a concept completely or am I overlooking a detail?

1. The problem statement, all variables and given/known data

The following questions deal with a pendulum in motion with angle not being its extreme end where v = 0 m/s

1. T is smallest when angle= ± angle not

2. The vertical component of tension is constant.

3. T = Mg at some angle between zero and angle not.

4. T is greater than Mg when angle=angle not

5. T is largest at the bottom (angle=0)

6. T equals Mg when angle = angle not

2. Relevant equations

sum of vertical forces = 0
T cos A = mg
sum of horizontal forces = 0
T sin A = F

3. The attempt at a solution

1. T is smallest when angle= ± angle not
True No motion occurs at this point so no centripital acceleration occurs

2. The vertical component of tension is constant.
True vertical component of T is always constant, it is equal to mg horizontal force always vary according to the angle

3. T = Mg at some angle between zero and angle not.
True at different points the system has the properties of T<mg and T>mg. You can obtain this change without passing through T=mg.

4. T is greater than Mg when angle=angle not
False T will be less than the weight at the top of the swing, because there's no motion and hence no centripetal acceleration

5. T is largest at the bottom (angle=0)
True The tension in a pendulum string will be greater than weight at the bottom of the swing, because it has to provide an upward net acceleration

6. T equals Mg when angle = angle not
False T < mg at the apex of the pendulums motion
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution