If a rocket is fired with a velocity, V=2gR near the earth’s surface and goes upwards, its speed in the inter-stellar space is

According to the law of conservation of energy[T.E]Surface =[T.E]interstellarspace ⇒−GMmR+12mv2=0+12mv12⇒mgR+12m(2gR)2=12mv12⇒12mv12=mgR⇒v12=2gR⇒v1=2gR