Rodger- Whiplash is a laymans term for a soft tissue injury to the neck, very rarely used by doctors as it has certain connertations to the patients, and legally. It basically means you have strained a muscle in your neck. You have muscles at the front and back of your neck, any of which you may strain by foreced hyerflexion or extension. This will settle down , but will get worse before it gets better. Lots of gentle movement, painkillers and it should be fine a week. DO NOT PUT A SOFT COLLAR ON, this will make things worse and give you a chonic stiff and painful neck.
Snowboard- Would ask for a second opinion from another GP, or a direct referal to an orthopeadic surgeon. Inability to fully extend at the elbow i.e straighten your arm IS NOT NORMAL. You may have a bit of bone in the joint or some scar tissue blocking it's range of movement. An MRI or an elbow arthroscopy would sort this out and get to the bottom of things. Any other symptoms like pain, locking or clicking?
Write back and tell me how things go,
Haka