Question

If a body is pushed once with a force ,will it accelerate for ever with no external force acting on it after that

Answer 1

You don't need a force to keep something moving. You just need a force to get it moving. Or to STOP it moving. In your day-to-day experiences, anything you get moving seems to come to a stop after you stop pushing it. That's because there are forces (friction) that cause it to stop. Without those forces, the object would just keep moving along.