M3: Motion in a vertical circle

(Paper attached)

Two questions:

Firstly, with vertical SHM (particle on string). If T=0, then do you assume it's at natural length? (Jan 07 Q7c - x value )


Also, Question 4 part c) - why isn't the component of velocity cos not sin?

Thank you

For the first question;

EDIT: Are you talking about time or tension in the first question? If its tension then yes at natural length there is no tension in the string if it is the vertical plane the particle is then acting under gravity alone.
If talking about time. The particle is released from point B initially so at time t=0 the particle is at B.

Second question;

It's hard to explain without a diagram but I assume you know the velocity acts through the line of the tangent to the circle. If you carefully draw out a diagram and make sure you get your angles right you will see its sin not cos

1 - I was talking about tension sorry!
2 - see attachment - is this the correct component?

Thanks

1 - I was talking about tension sorry!
2 - see attachment - is this the correct component?

Thanks