Speed of Pendulum Bob at Lowest Point

[jamman751]

Homework Statement

A simple pendulum consists of a bob of mass 1.8kg attached to a string of length 2.3m. The pendulum is held at an angle of 30° from the vertical by a light horizontal string attached to a wall. If the horizontal string is cut close to the bob and the pendulum swings down, what is the speed of the bob at its lowest point.

The exact problem can be seen here. Its problem 2c. http://www.collegeboard.com/prod_downloads/ap/students/physics/ap05_frq_physics_b.pdf

The weight of the bob is 17.64N. The tension in the horizontal string is 10.18N. The tension in the 2.3m string is 20.36N.

Homework Equations

The relevant equations are all at the top of the pdf given in the link. This is a AP Physics B problem so calculus isn't allowed.

The Attempt at a Solution

My attempts all involve me attempting to find the time to swing or the angular acceleration which I can not find. I am not sure if the angular acceleration or the tangential acceleration is zero at the bottom of the swing.

 

[omoplata]

Consider conservation of energy.

 

[jamman751]

Consider conservation of energy.

I can't use that because we haven't learned it yet.

 

[omoplata]

The only other way is to find the acceleration of the bob and integrate. But you say calculus isn't allowed.

 

[Redbelly98]

Consider conservation of energy.

I can't use that because we haven't learned it yet.

Then you can't solve this problem -- yet. But since conservation of energy is part of the AP Physics B curriculum, then it is totally fair to expect students to use that method to solve this problem.

It is pretty clear to people familiar with the AP Physics B curriculum that conservation of energy is the way to solve problem 2c.

p.s. welcome to Physics Forums, janman751