First, as Justin Cave noted, you are only taxed on the gains on property that is sold, and there is usually no gains for cars and furniture. There are often gains for houses. Are you selling a house? If not, this question is likely moot.
For your question, the main issue here is whether you are a resident alien or nonresident alien on the date your property is sold. Residents are taxed on their worldwide income, but nonresidents are only taxed on their US-sourced income, and gains from selling a house would be sourced where the house is. (A similar rule would apply to state taxes for residents and nonresidents of the state, but Florida doesn't have an individual state income tax, so we don't need to consider that.)
For the rules on determining whether someone is a resident alien, see Publication 519. A foreigner is a resident alien for a given year if they pass the Green Card Test or the Substantial Presence Test for the year. The person here never had a green card, so it's only the Substantial Presence Test that matters.
The Substantial Presence Test is passed if (the number of days you are present in the US that year + 1/3 the number of days you are present in the US the previous year + 1/6 the number of days you are present in the US the year before that) is greater or equal to 183 days (i.e. more than half the year). It does not depend on whether you have a visa, how long you are staying, or what status you have or even if you have a status (except that certain statuses, like students and exchange visitors, are exempt from the SPT for a number of years, but that is not relevant here).
So assuming you have never been in the US before, and if you arrived in the second half of the year, you would not pass the SPT in the year of arrival, and you would thus be a nonresident alien for that year (although you can choose to become resident for the part of the year after you arrived by using First-Year Choice). If you arrived in the US in the first half of the year, you would pass the SPT in the year of arrival, and thus be a resident alien for that year, although according to the First Year of Residence rules, your residency start date would only be when you arrived (thus you would be dual-status).
Since the date of the sale is soon after you arrived (and I assume it is in the same year), it would be subject to US tax if you arrived in the first half of the year, but not subject to US tax if you arrived in the second half of the year.
