Physics Doubt. November 2010.Paper 33

[Rahma Magdy]

Hello..
I have a physics exam tomorrow and I have a doubt with a question is paper 33 November 2010
Q1)a)iii)
http://www.xtremepapers.me/CIE/Cambridg ... _qp_33.pdf
...
I really hope someone would help me
Thanks in Advance