Angular Momentum (pendulum) Help

[tdub96]

Homework Statement

a 1.5 kg pendulum bob swings in a vertical circle at the end of a 2m long string with negligible weight. If the bob is dropped from a height in which the string is horizontal and taut, what is the angular momentum at the bob's lowest point (in kgm/s^2)?

a 40
b 10
c 30
d 20
e 50

Homework Equations

L=Iw
L=mrv
L(initial)=L(final)

The Attempt at a Solution

I tried using the formula v²=v_o²+2aΔy to solve for linear velocity first. It would be v= sqrt(2*9.8m/s/s*2m) because it falls the length of the string to reach the horizontal correct? From there, I calculated v to be 6.26m/s, and then subbed that into L=mrv for a final answer of 18.78kgm²/s, but its a bit off the possible choices and I'm skeptical of my work.

Any help would be greatly appreciated!

 

[fluidistic]

Homework Statement

a 1.5 kg pendulum bob swings in a vertical circle at the end of a 2m long string with negligible weight. If the bob is dropped from a height in which the string is horizontal and taut, what is the angular momentum at the bob's lowest point (in kgm/s^2)?

a 40
b 10
c 30
d 20
e 50

Homework Equations

L=Iw
L=mrv
L(initial)=L(final)

The Attempt at a Solution

I tried using the formula v²=v_o²+2aΔy to solve for linear velocity first. It would be v= sqrt(2*9.8m/s/s*2m) because it falls the length of the string to reach the horizontal correct? From there, I calculated v to be 6.26m/s, and then subbed that into L=mrv for a final answer of 18.78kgm²/s, but its a bit off the possible choices and I'm skeptical of my work.

Any help would be greatly appreciated!

Looks ok to me. Maybe they took g as 10 m/s² which should be a slightly greater velocity and hence angular momentum.

 

[tdub96]

Using 10m/s/s comes out to be 18.97, which is closer, but I am still not confident in that. I'm going to keep trying some stuff, if anyone has anything to contribute please do so!