[填空题]
Suppose David puts a 0.5 zg 1csykz215c0-kg rock into2k1locd p.x0yckea5oz d1k6; a sling of length 1.5 m and begins whirling the rock in a nearly horizontal circle above his head, ac a k l;xe5pkoyo 0z26dc1d1.kccelerating it from rest to a rate of 120 rpm after 5.0 s. What is the torque required to achieve this feat, and where does the torque come from? $m \cdot N$