Question

A question related to forces and yeah, the answer is B, but how do you get that step by step?:/
Thanks in advance.
In attached file.

Answer 1

Torque disc = 900 N x 0.2 m = 180 Nm
From force couples T=F.d (d=perpendicular distance between two forces)
T=F.1.2 = 180 Nm ==> F = 150 N

Answer 2

I guess one of your passage is wrong
Actually T=2F*0.6, not F*1.2 (is the same but conceptually is different)
So
\[\tau_1=\tau_2\]
the angles between F and R are all pi/2:
\[F_1*R_1=2(F*R_2)\]
\[F=(F_1R_1)/(2R_2)\]
F1=900, R1=0.2, R_2=0.6 and u get it ;)

Answer 3

@Armi and @the_duro
Thank you both so much ! (:

Answer 4

Armi i was not wrong about T=Fx1.2 because of couple forces.
http://en.wikipedia.org/wiki/Couple_(mechanics) read the simple couple part.