Answer:
You use a knife to slice my head and weep beside me when I am dead.
I help engines spin and pants stay up. What am I?
I am gentle enough to soothe your skin, light enough to fly in the sky, strong enough to crack rocks. What am I?
I am not alive but I can die. What am I?
I ask no questions, but receive a lot of answers. What am I?
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.