Answer:
Each nitrogen molecule consists of two atoms of nitrogen that are bonded by a triple covalent bond. This is because each nitrogen atom has 5 valence electrons. Each atom can complete its octet by sharing three electrons.
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Taking the copper wire, he has to wind it around the nail made of iron. After which, he then connect both ends of the copper wire to the battery, so an electric charge travels through the wire. This is the basic electromagnet. Since a current is now flowing through the wire, a magnetic field is produced. Placing the electromagnet near the mixture of copper and iron, the magnet should attract the pieces of iron, as iron is more magnetic compared to copper. This is done over a period of time, so that only the copper pieces are left in the mixture.
Imagine an object is moving in one dimension on a number line, and for this we'll say that the numbers on the line are a metre apart. If the object moves from 2 m to 7 m, the change in position is 7-2=+5 metres. But if the object moves back from 7 m to 2 m, the change in position is 2-7=-5 metres. since

, and time is always positive, velocity will be positive in one direction and negative in the other direction.
Answer:
Work done W =1406.25 J
Explanation:
Work done on a body can be calculated using newton's 2nd laws:
F=ma
Hence acceleration of the block is given by:
Displacement of the object is given by:

Substitute the values
Now work done is given by:
W=F.S
W = 25×56.25
W =1406.25 J