Which of the following is a good insulator? wire, doorknob, plastic, nickle

I'm thinking it's 2 you are asked to explain the earth's magnetic field. which is the best reply? 1. the earth's magnetic south is similar to the north pole of a magnet. 2. the earth's core has a strong magnetic charge similar to the south pole of a magnet. 3. the earth's geomagnetic south is similar to the south pole of a magnet. 4. the earth's magnetic charge is not centered at either pole; it varies based on location.

Aforklift raises a box above the floor and does 2,000 j of work. if the forklift motor consumes 3,000 j of electrical energy from the battery to raise the box, what is the efficiency of the lift?

Paul and ivan are riding a tandem bike together. they’re moving at a speed of 5 meters/second. paul and ivan each have a mass of 50 kilograms. what can paul do to increase the bike’s kinetic energy?