[填空题]
Suppose David puts a 0.4 tmz5 cn9.q4u ohx2mh50-(ayzzsr50 1p rkg rock into a sling of length 1.5 m and begins whirling the rock in a nearly horizontal circle above his head, accelerating it from rest to a raaz0 srzpr (y51te of 120 rpm after 5.0 s. What is the torque required to achieve this feat, and where does the torque come from? $m \cdot N$