# Speed of Pendulum Bob at Lowest Point

• jamman751
In summary, the conversation discusses the problem of finding the speed of a bob in a simple pendulum at its lowest point. The bob has a mass of 1.8kg and is attached to a string of length 2.3m, held at an angle of 30° from the vertical by a light horizontal string attached to a wall. The weight of the bob is 17.64N and the tension in the horizontal string is 10.18N. The conversation considers different methods of solving the problem, including using conservation of energy which is part of the AP Physics B curriculum. However, since calculus is not allowed, the person is unable to find the time or angular acceleration and therefore cannot solve the problem at this
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 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.

Consider conservation of energy.

omoplata said:
Consider conservation of energy.

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

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

omoplata said:
Consider conservation of energy.

jamman751 said:
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

## What is the speed of a pendulum bob at its lowest point?

The speed of a pendulum bob at its lowest point is dependent on the length of the pendulum, the acceleration due to gravity, and the angle at which it is released. It can be calculated using the equation v = √(gL(1-cosθ)), where v is the speed, g is the acceleration due to gravity, L is the length of the pendulum, and θ is the angle at which it is released.

## Does the mass of the pendulum bob affect its speed at the lowest point?

The mass of the pendulum bob does not affect its speed at the lowest point. The speed is only dependent on the length and angle of release. This is because the mass of an object does not affect the acceleration due to gravity.

## What happens to the speed of a pendulum bob at its lowest point if the length is increased?

If the length of the pendulum is increased, the speed of the pendulum bob at its lowest point will also increase. This is because the longer the pendulum, the greater the distance it must travel in a given time, resulting in a higher speed.

## Is the speed of a pendulum bob at its lowest point constant?

No, the speed of a pendulum bob at its lowest point is not constant. It is constantly changing as the pendulum swings back and forth. However, if the angle of release and length of the pendulum remain constant, the speed at the lowest point will remain the same for each swing.

## How does air resistance affect the speed of a pendulum bob at its lowest point?

Air resistance can decrease the speed of a pendulum bob at its lowest point due to the force it exerts on the bob as it swings. The greater the air resistance, the more it will slow down the pendulum's swing, resulting in a lower speed at the lowest point.

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