# Pendulum and string problem

1. Oct 19, 2005

### lonely86driver

i dont know if i'm making this look easy or hard but heres the question

A pendulum made of a string of length 10.4m and a spherical bob of mass 2.2kg is able to swing in a vertical plane. The pendulum is released from an angular position 41* from vertical. The string hits a peg located a distance 6m below the point of suspension and swings about the peg up to an angle "a" on the other side of the peg. the bob proceeds to oscillate back and forth between these two angular extremities. acc. of gravity is 9.8 m/s^2. what is the period of the pendulum plus the peg system shown above.

since period only depends on length of the string and acceleration due to gravity
this is what i was thinking about the problem. i just add two periods togethers. but then reading the problem again its sounds like i need to find the period of the second system in order to find the complete period of the entire system.

it sounds like the second system is a torsional pendulum problem so i might have to find the period for that.
i wish i had a pic to post up but i dont have it on my computer.

2. Oct 19, 2005

### Tom Mattson

Staff Emeritus
It's nothing like that. You have a simple pendulum before and after the string touches the peg.

Try to answer the following questions, in order.

1.) How long does it take for the bob to drop from its release point to the peg?

2.) What must the angle $a$ be after the string hits the peg? (Hint: What quantity must be conserved here?)

3.) How long does it take for the bob to get to the angle $a$ after the string hits the peg?

3. Oct 19, 2005

### lonely86driver

ahhh i see now thanks

4. Oct 19, 2005

### Tom Mattson

Staff Emeritus
Let us know if you get stuck.