This may sound like a silly question but does size effect speed ? for example if some generation were to build a rocket the size of planet earth,would that then be able to travel faster than the speed of light ?

Nothing travels faster than the speed of light in any reference frame.

Technically mass doesn't affect speed; it affects acceleration according to F=ma.

This may sound like a silly question but does size effect speed ? for example if some generation were to build a rocket the size of planet earth,would that then be able to travel faster than the speed of light ?

No, as Facial puts it in its proper context but allow me to expand the reason a little bit - in order to get thing like a ship to move, it needs to expend energy as thrust or have energy applied too it, as in chucking it.

Energy can take many forms, one of them being Light - and actually, when your talking about pure energy, light itself is one of the ways pure energy expresses itself. It's fast, but but it has a finite speed - that being, the Speed of Light.

Everything else travels at a speed either equal to or less than the Speed of Light.

Now, getting back to moving your ship - in order to move it, you have to use energy to do it. But since energy itself has a top speed of fast but no faster than it doesn't matter how much energy you use - energy can't possibly travel any faster than it itself is capable of travelling.

Consequently, y'could build a rocket as big as the entire solar system if you wanted and all the energy implied contained with in - that ship still isn't going to travel one jot faster than energy itself is capable of travelling - the speed of light.

Hope that helps. A ;)