[填空题]
A person exerts a force of 55 N on the end of a door 5rtml,jxa /n 3l; qfj pr8i1n2n7t5ry)tm9ve 74 c qs2 erjq9p9wqg(0 ,atm wide. What is the magnitude of the torque if the force is exqsp9wtq r 9j, (qag0e2erted
(a) perpendicular to the door $m \cdot N$
(b) at a 45 $^{\circ} $ angle to the face of the door? $m \cdot N$