That's exactly right. Well done!

Bob

]]>d^3s/dt = -3cost - - sint = -3cost +sint

if this isn't right I don't know what is.

]]>Your image is somewhat squashed up and with no equals. The dy should be ds. This is what I think you meant:

This is correct

This first term is correct but the second bit is not.

But this is not right. The sign is wrong and there shouldn't be a 3 there.

And this has gone completely wrong. You've lost the 3 from the first term and the error above has made the second term wrong too.

I suggest you have a go at d2s/dt^2 again and I'll check again.

Bob

]]>I have this question and given my answer for second and third derivatives. not sure if its right though]]>