Both are good and both are used in day to day speech. Probably "you MUST wear a seat belt" carries a little bit more force - or more emphasis. For example: The policeman says you must wear a seat belt If your dad drives you to school then you have to wear a seat belt in the car Hope that helps. The difference is subtle

If you're trying to state your feelings you should use MUST On the contrary, if you are trying to express the obligations you should use HAVE TO. Just compare these two sentences: You must wear a seatbelt to reduce the consequences of an accident (you believe in its effect) You have to wear a seatbelt not to have a fine from the police. (you believe that it's an obligation)

The subject regarding the use of seatbelts relates to road safety, which falls within the domain of Health education. The correct answer to the multi-part question would be: 'You must use your seatbelt and failure to do so may result in a traffic ticket'

For describing obligation in specific situations, "to have to (do)" is common and practical because "to have to (do)" has past, present, and future forms. Examples: My boss was away on a business trip, so I had to run the department meeting in his absence. My boss will be away on a business trip, so I will have to run the department meeting in his absence. For describing obligation in timeless situations, "must (do)" expresses obligation, often imposed by the government or an employer. Examples: All professional truck drivers must have a valid class 3 truck driver's licence.

They both can be used, but you have to wear a sest belt is more common