In a compressing spring in a toy dart gun, 0.8 j of work is done. when the gun is fired, rhe spring gives its potential energu to a dart with a mass of 0.04 kg. what is the darts kinetic enegy when it leaves the gun?

0.8 J

Explanation:

According to the law of conservation of energy, all the elastic potential energy stored in the spring is converted into kinetic energy of the dart:

where we have

is the elastic potential energy of the spring, where k is the spring constant and x is the compression/stretching of the spring

is the kinetic energy of the dart, where m is the mass and v is the speed

The elastic potential energy of the spring is equal to the work done in compressing it, so

U = 0.8 J

and according to the law of conservation of energy, the kinetic energy gained by the dart is exactly equal to the potential energy stored in the spring:

K =  U =0.8 J

r=rho l/a where a is the area, l is the length and rho is resistivity so the greater the area the lesser the resistance thats why the earth pin is thicker bcos current follow the shortest path, so less resistive .