How Does Tension Direction Affect Torque in a Pulley System?

[kari82]

Block 1 has mass m1 = 460g, block 2 has mass m2 = 500g, and the pulley, which is mounted on a horizontal axle with negligible friction, has radius R = 5.00cm. When released from rest, block 2 falls 75.0 cm in 5.00 s without the cord slipping on the pulley. (a) What is the magnitude of the acceleration of the blocks? What are (b) tension T2 and (c) tension T2? (d) What is the magnitude of the pulley's angular acceleration? (e) What is its rotational inertia?

I have solved most of the problem, but I just have one question about e. Solving the previous questions we get that angular velocity is 1.2 rad/s^2, T1=4.5 N and T2=4.87 N. I know that I=torque/angular velocity. The book says that the net torque in this case is r(T2-T1).. Here is my question. Why is T1 negative?

Thanks!

 

[cupid.callin]

because T1 will tend to rotate the pulley in opposite direction as compared to T2

also you can use cross product rule to find that direction of the two torques in opposite