Final answer:
While the crane and power line scenarios address various physics principles, none provide the specific safety distance for crane operations near power lines, which depends on local regulations and voltage levels.
Step-by-step explanation:
The question asks how much distance must a crane keep when working near power lines. However, the provided information references several different physics problems involving cranes, power lines, and magnetic fields, none of which directly state the required safety distances for cranes operating near power lines. In reality, the safe distance a crane must maintain from power lines is determined by safety regulations which usually vary depending on the voltage of the power lines. These regulations are designed to keep workers safe and avoid electrical hazards. Since the provided information does not mention these specific guidelines, it's important to consult local regulations or workplace safety standards for the exact distances required.