Cual es la principal fuente de energia mas utilizada en un generador electrico

What happens in a global convection cell

Could someone . i have tried to solve myself but my calculation is off

A1,700kg car is being used to give a 1,400kg car a push start by exerting a force of 140n the impulse on the smaller car during the 30.0s of contact is +670kg*m/s. what is the impulse of the smaller car on the larger car? -814 kg*m/s 0kg *m/s -670kg*m/s -550kg*m/s