Many gates at railway crossings are operated manually. a typical gate consists of a rod usually made of iron, consisting heavy weight. what is the need for the heavy weight at one end of the rod? ?

  Making the crossing gate balanced makes the mechanical drive simpler and less expensive to operate.

Explanation:

See the attachment for a picture of what we're talking about.

The gate must be rotated up and down. That rotation is easier if the mass being rotated is balanced about the center of rotation. Less torque (and work) is required to create the desired motion.

Iwas going to ask that quesytion  sorry dude i dont  know : (    : /

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current