JEE Advanced Model Paper 1 with solutions for online practice

Forces acting on the block are (a) the tension T and (b) the weight W. At the lowest point, the resultant force is T - W towards the centre. As the block is going in a circle, the net force towards the centre should be mv2/r with usual symbols. Thus,
T - W = mv2/r
Or , T - W + mv2 / r = 10 N +

(1Kg)(2ms−1)2

0.2m

= 30N
We have Y =

T∕A

l∕L

Or,
l =

TL

AY

=
= 5 × 10−5 × 20 cm = 10−3 cm