# sir in p-197 of HCV i m confused in the concept of two problems so will u plz illustrate me the exact concept with DETAILS in q36 and q38 inq no. 36 in writing the eqn for torque they have first written the force which rotates the pulley anticlockwise is written first but in q 38 the tension which rotaes the pulley clocwise is writen first and after that anticlecwise rotating force is wriiten plz tell me how to know that wchich force is to be written first in writing equation for torque

Sudheesh Singanamalla
114 Points
12 years ago

Ritvik Gautam
85 Points
12 years ago

In Q. 36, It is assumed that M>m... Hence, the block with mass M will go downwards while the block with mass m will go upwards. In such a motion, the pulley will rotate anti-clockwise direction.

In Q.3The 4 kg block will go downwards and the 2 kg block will move upward. Hence, In such a motion, the pulley will rotate in clock-wise mannar.

DIVYANK DUVEDI
33 Points
12 years ago

to all those replied my post this is not my doubt

ihv already solved this problem but main confusion is as follows

whenever we wite eqn for pulley sometimes we are writing those tension forces >say it is t1<  which tries to rotate the pulley in anticolwise direction followed by the other tension force which tries to rotate it in clocwise direction<say this is t2>

eqn becomes t1-t2=Ia/R2 ..........................(as in eq5 of post no 1)

but in some problems if t1 rotates clockwise and t2 rotates anti clocwise <note care fully>

eqn becomes t1-t2=Ia/r2

this is what in eq2 of post 1 of this q

that is why i m confused abt both these problems

so in next reply plz give the proper answer so that i can independently solve any type of problem

thnx a lot but plz reply in detail by writing all those concepts that you must recall before writing this eqn for rotating pulley